tree-view is a pane that displays a hierarchical list of items. Each item may optionally have an image and a checkbox.
Callbacks can be specified as for other choice classes. Additionally you can control how the nodes of the tree are expanded, and there is delete-item-callback available for use when the user presses the Delete key.
Tree views are used in the LispWorks IDE, for example in the Output Data view of the Tracer tool and the Backtrace area of the Debugger and Stepper tools.
CAPI User Guide and Reference Manual (Macintosh version) - 3 Aug 2017