I attached a sample project illustrating how you can get the CheckedItems collection from the RadTreeView and use it as the ItemsSource collection of a ListBox.
Please take a look at the example and let me know if this is what you had in mind.
the Telerik team
Do you want to have your say when we set our development plans?
Do you want to know when a feature you care about is added or when a bug fixed?
Telerik Public Issue Tracking
system and vote to affect the priority of the items.