command does exist, actually. The help topic just does not seem to be updated with new command events recently added to RadTreeList. Most RadGrid events are available in RadTreeList in the same form and API.
As for inserting a new item in RadTreeList from RadToolBar items, you can use RadTreeList.InsertItem()
for inserting a root item, or TreeListDataItem.InsertChildItem()
for inserting a child item from the specified data item. You call any of these methods from an outside event handler on clicking the toolbar item.
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