I was not able to Bind Checked Items in RadTreeView to a list of predefined entities.
What is the preferred approach bind the list of hierarchical data in two way mode to checked Items in tree. So that check/uncheck will update the bound list.
It is for Silverlight and explains how to use ContainerBindings, which is almost the same as using Style bindings in WPF.
The article explains how to bind the IsSelected and IsExpanded properties of RadTreeViewItem, but does not explain how to bind the CheckState. That is why, after going through the article, you can take a look at the attached sample projects.
The ContainerBindings.zip contains a Silverlight project demonstrating the functionality you are looking for, and StyleBindings.zip is its WPF equivalent.
Give it a try and let me know how it works for you.