Description
A tree is a hierarchical List, allowing users to expand and collapse nodes to show or hide nested items.
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Types
Usage | Image | |
Single selection tree | | |
Multiple selection tree | For multiple selection trees, smart selection mode will be applied. See the Interaction section of Lists for more information. |  |
Usage & Behavior
Trees are used to navigate within hierarchical lists of objects (e.g. organizations), and then to select one or more items in order to filter content or show additional information.
They usually appear inside a Filter Pane, a Details Panel, or a Widget.
General guidelines
Structure
The tree consists of:
Leaf nodes
A leaf node is an object that contains data.
Each leaf node consists of:
a title. Long titles can be truncated and a Tooltip can be used on hover.
an optional icon, representing its type (e.g. a document). If all nodes are of the same type, the icon should not be used.
Where a leaf node represents an employee, an avatar image may appear instead of an icon.
Container nodes:
A container node is an object containing other items (e.g. a folder).
Each container node consists of:
a triangle toggle button, to the left of the title.
an icon.
a title.
Container nodes have 2 states:
Collapsed, when all child items are hidden. In this case, the triangle toggle button points towards the node title.
Expanded, when all or some levels of child items are shown. In this case, the triangle toggle button points downwards.
If the icon representing a container node is a folder, it may also have the 2 states, closed (when collapsed) and open (when expanded).
In some cases, a counter will appear next to the node title, showing the number of contained items.
A root node (optional)
A single node that appears at the top of the tree and contains all other nodes.
It appears when relevant or when the user is allowed to select all items at once.
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Multiple Selection
Where multi-selection is used, each node will have a Check Box which appears on hover, allowing the user to select and deselect it.
Default State
Where a root node exists, it will be expanded by default, showing the second level of nodes.
Where there is no root node, the list can be either entirely expanded, entirely collapsed, or have only the first node expanded and the other nodes collapsed. This depends on the specific needs and expected usage.
Content
Nodes should be ordered alphabetically, to allow users locating specific items quickly.
An exception to this is time-related lists, which should be ordered chronologically, with the most recent item first.
Logical. Sort options into a meaningful order. For example, group related options together, and order by the most common to least common.
Alphabetical. If there are more than 8 options available, sort them alphabetically. This helps the user to find the right option quickly. Sort currencies, names, and similar content alphabetically.
Numeric. Sort numeric values in a sequential order, with the lowest number first.
Chronological. Sort time-related information into chronological order, with the most recent first.
States
Regular |  |
Hover |  |
Active |  |
Disabled | |
Focused |  |
Focused, Hover | |
Focused, Active | |
Focused, Disabled |
Interaction
Hovering over a truncated node title will show a Tooltip containing the full title.
Clicking on a node (including the title and the icon) will select it. Any previously-selected nodes will automatically be deselected.
Clicking a triangle toggle button or double-clicking a container node will:
toggle the node between the collapsed and expanded states. When loading the content of the node takes more than 1 second, a Progress Indicator will appear.
toggle the triangle button between states.
Where multiple selection is used:
Clicking a check box will select or deselect the item, including all child items where they exist, regardless of other selections.
If only some of the child items are selected, the parent item will be in a partially selected state.
See the Interaction section of Lists for more information on selecting items.
Single select: One item of the tree can be selected. To select an item, click anywhere on the item row.
Multiple selections: Allow the selection of one or more items. For this, the tree provides checkboxes on the left side of each line item. Each item is selected independently of the others
Single Selection | Multiple Selection Mode |
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Single selection is activated by selecting the node label. Selecting the node label will select the node and un-select previously selected node. | On mouse hover a node, a check box is displayed. If the user checks it he is placed in a multi selection mode. Multi selection mode can also be activated by using Ctrl/Shift while selecting the node label. On this mode, clicking the label/check box will perform multi select. Only once the apply is pressed the action is executed (whatever the corresponding action is). Selecting a parent node through the check box will select its descendants as well. Unselecting some of the descendants will place the parent node in mixed state. |
Drag and drop, Please refer to the Drag and drop pattern
Best practices
Use:
when there is a need to select one or more items from a hierarchical list.
Don't use:
where there is no real hierarchy → use a List instead.
to select values in a form or where the number of items is small → use a Drop-down Menu instead.
General
Try to avoid trees with too many hierarchy levels. How many are reasonable?
An optional Search field can be used for large trees, to help the user find items easily.
Accessibility compliance
Unless otherwise specified, see our general compliance information in Fundamentals - Accessibility.
Design
Zeplin link | Screen thumbnail |
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Single Select |  |
Multi Select |  |
Smart Select |  |
Tree - Organization |  |
Code
