You can easily achieve such functionality(and even extend it) by wrapping our SitefinitySiteMapDataSource control (the one that we're using for binding our navigation controls) and a RadTreeView inside a user control. I've prepared a sample user control for you (attached to this reply, along with a short video
demonstrating the control functionality), which should duplicate the desired functionality. If there's anything else we can help you with, or you need any additional information regarding the user control, please do not hesitate to get back to us.
the Telerik team
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