The treeview needs to be able to get the client-side object of other treeviews through the DOM, in order to support drag&drop of nodes between treeviews. Because we don't have the client-side object, we cannot guess what the custom name is (so that we get the proper object). Therefore, if you need to extend an existing widget (through inheritance rather than composition), don't change its name. Another option would be to attach the same client-side object to the data("kendoTreeView").