Bind to a Selected Item
RadTreeView exposes SelectedItem property, which is a DependencyProperty and can be used in a data binding.
<telerik:RadTreeView SelectedItem="{Binding SelectedItem, Mode=TwoWay}"/>
If you want to bind to the RadTreeViewItem's IsSelected property when your treeview is data bound to an object, then you need to use an ItemContainerStyle.
<telerik:RadTreeView>
<telerik:RadTreeView.ItemContainerStyle>
<Style TargetType="telerik:RadTreeViewItem">
<Setter Property="IsSelected" Value="{Binding Path=Select, Mode=TwoWay}" />
</Style >
</telerik:RadTreeView.ItemContainerStyle>
</telerik:RadTreeView>
When using NoXaml dlls, the Style set to the ItemContainerStyle property should have its BasedOn property set to {StaticResource RadTreeViewItemStyle}.