problem with treeview

Hello !

I have two treeview in a  view and I add items to the treeview manually . I use Treeview_SelectedItemChanged event. When i click the second treeview the last selected item in the first treeview is not get unselected. If i click that item in first treeview again then its not doing it purpose. So please tell me how to get rid of this problem. There is no IsSelected function for manually added items in Treeview.

Thanks for your help !