Tree: A New Dimension in Outlining

Creating an outline is a handy way to organize, plan and brainstorm. One of the strengths of the outline is its hierarchical linear relationship among the topics in the list. That can also be one of its limitations, as the list can become long and start feeling one-dimensional.

The outliner Tree tries to remedy this with a twist on the standard outlining format. In Tree you can expand your outlines horizontally, as well as vertically. Today we’re going to take a look at whether or not the approach Tree takes actually bears fruit.

Tree outliner

Tree is the work of Japanese developer Kazuhiro Kawana, whose website is called Top of Tree. You will need to download and install Tree the “old-fashioned” way, because it is not yet available on the App Store, although Kawana is planning to one day get it there. This is a review of version 1.7.3, which was released in early July. You can download and run a trial version of Tree for 14 days.

Tree has two viewing options for your outline: Listview and Treeview. If you are familiar with basic outlining applications, such as Opal, you will be pretty comfortable in Listview. Treeview, on the other hand, is something different. In Treeview your outline expands horizontally to the right, like a flow chart or diagram. Because Tree is first and foremost an outliner, I’m going to look closely at Listview and evaluate Tree for its ability to help you build useful outlines, before I move on to examining Treeview.

Tree outliner 2

Tree outliner in "Listview" mode

Outlining in Tree

The first thing I do when evaluating an outlining application is to just start using it. I want to find out how quickly I can become familiar and comfortable with the keystrokes necessary to create an outline. I don’t want to be thinking about which keys I need to press to create a sub-topic, or fumbling around trying to move a sub-topic from one topic to another. The more “invisible” the application is, the more effective it is for capturing thoughts and ideas.

Tree isn’t hard to get used to. I was able to quickly get the hang of its keystroke commands, most of which are intuitive once you know the scheme. To add an item as a sibling (that is, at the same level), use the command and return keys together. To create a daughter item of the currently selected item, use the command and K keys together. Alternatively, you can change a preference so that simply pressing return creates a new sibling item, which can be made a sub-topic with the tab key.

Tree outliner screenshot 3

Tree provides multiple options for re-organizing the notes in your outline.

Likewise, moving items around the outline is pretty easy too. Use the arrow keys in conjunction with the control and command keys. I would prefer it if only one of those two keys were needed, but this is acceptable.

Inline Notes

Okay, now that I know I can use Tree efficiently to build my outlines, it is time to delve into its other outlining capabilities. First among these is the pleasant surprise that Tree supports inline notes. That is, you can create additional text for each of your topics and view it “inline.” This may not be an essential feature for outlines, but it provides a more natural reading and reviewing experience that I appreciate. And it is not very common in outliners today.

Tree outliner screenshot 4

In Tree outliner, you can view your topic notes inline.

To create an inline note, just press the command and single-quote keys, or use the tool bar button. You can choose to hide notes individually by clicking the little note icon that lives to the right of each note. By default, the note text is grayed out, but you can change this using preferences.

Checkboxes, Numbering and Labels

You can choose to view or hide checkboxes and numbering for your Tree outlines. Neither checkboxes nor numbering is a particularly robust feature of Tree, but they are both serviceable. You cannot selectively apply checkboxes, so every item in your outline will have them or none. I can live with this all or nothing approach, but I’d be more impressed I could apply them to specific sets of topics.

Topic numbering is similarly limited. You can select what type of alpha-numeric character to use as the number for each topic, but you can’t really change the style. In other words, I can pick numerals, roman numerals, upper-case letters, etc… but they apply to the entire outline. I can’t make the top-level topic labels roman numerals, with the sub-topics uppercase letters, and sub-sub-topics regular numerals, as is a common format. That is not a severe limitation, but it may make Tree less useful for formal outlining, where the only style that really makes sense is numerals.

Tree outliner detail 5

Limited topic numbering options can lead to odd-appearing outlines.

Tree also sports a simple labeling scheme that allows you to color-code the reveal arrows. You can choose up to seven different colors and give them custom meanings — urgent, important, etc.

Multiple Windows and Tabs Help You Focus

Hoisting is a very helpful feature in outliners allowing you to focus in on one topic and its sub-topics. Tree accomplishes this with a unique approach. Tree allows you to open a topic and its progeny in a separate window or in a separate tab. In this way you can easily reference the entire outline while working on just a section of it. When you make this selection (either tab or window), the topic in the original window is folded, so the sub-topics are hidden and you cannot reveal them until you close the family window/tab. You can open as many separate windows and tabs as you need.

Tree outliner screenshot 6

Open sub-sections of your outline in separate tabs or windows.

Treeview Provides a New Perspective

So far we’ve seen that, as a straight outlining tool, Tree is quite functional with some nicely implemented properties. However, the feature that truly sets Tree apart, the one that gives it its name, is the Treeview mode.

Treeview mode switches the outline from a standard vertical layout to one that stretches out horizontally, more like a diagram than an outline. In Treeview, each succeeding generation (or topic level) is exposed in columns and connected by lines. Once in Treeview, your outline takes on a whole new dimension.

Tree outliner screenshot 7

In "Treeview" mode, you can view your outlines horizontally, like a flowchart or diagram.

Treeview is a very flexible mode. When you invoke Treeview, the topics that were revealed unfold into separate columns; those that were concealed remain so. You can choose to reveal or conceal any of the topics. You can even see some topics in standard outlining mode while others are unfolded into the diagram.

Treeview can be applied tab by tab or window by window, so that in one tab you can see your standard outline, while in another, you can view a topic family in Treeview mode.

It’s this later capability that gives Tree its real power, I think. Viewing the entire outline as an expanded diagram doesn’t seem to me to be particularly useful, as the screen becomes overly cluttered. But being able to view sections of it this way could be very handy for various types of planning, writing and study.

Flexibility to Mix and Match Views

While I find Treeview an intriguing feature, what is most impressive about Tree is how the developer has built it so you can combine these various views. See part of your information in standard outline view, while another branch is expanded horizontally.

Tree outliner screenshot 8

In Tree outliner, it is easy to focus on one section of your outline, with as much detail as needed.

Tree outline detail

Closeup detail of a Tree outline in Treeview mode.

Exporting to Other Applications

For the most part, outliners are useful for the beginning of projects, for collecting thoughts, structuring a writing project. This means that a good outliner should be able to export its data into formats useful in other applications. Tree scores fairly well in this aspect. You can export your outline to formatted text or plain text, for continued work in your favorite word processor.

Tree outliner review screenshot 10

Formatted text exported from Tree to TextEdit.

Tree also exports to Outline Processor Markup Language (or OPML) files. OPML is a standard file format that can be opened or imported by most quality outliners, which means your Tree files can easily be shared with a variety of other outliners, including OmniOutliner and Tinderbox, notes and all.

Tree review screenshot 11

Exporting to OPML format, you can open your Tree outlines in Tinderbox...

Tree review screenshot 12

... in OmniOutliner Professional.


Tree is not a power outliner along the lines of Neo. It does not have cloning of items, meta data, or very robust numbering options. It doesn’t do tagging and you can’t include images or attachments. You also cannot adjust the format by level — that is, you can’t set the Tree to make level 1 items bold and 14 point text, and level 2 items underlined and 12 point text, for example.

But Tree does provide unique perspectives on your notes with its Treeview mode and flexible combinations of views. It would make a fine choice for those who need a basic outliner for simple to moderate outlining tasks. And the price is low enough at $24.99 that Tree could be a nice supplement to a more powerful outliner for those intrigued by its multi-dimensional viewing options.


Tree is a capable outliner lacking the more advanced features of some power outliners, but with the addition of a flexible, horizontal view of your topics, which makes it unique in its class.