In this post, Phil Middlemiss describes an attached-behavior for a TreeView control that allows you to achieve two-way binding on the SelectedItem property.
Source: Silverlight Scratchpad
In this post I described an attached behavior that lets you achieve two-way binding on the TreeView.SelectedItem property. The behavior is especially useful if you are using the MVVM pattern to keep your views and view models separate, and want to avoid code in the View’s code-behind file.