By default all the nodes of the WPF tree view is selectable. If some how we had a requirement that the roots nodes can not be selected rather only the child nodes will be selectable we need to customize one single property “focusable”. If we set the focusable property of any node to false then the node will not be selectable. pretty small thing but worth sharing because in MSDN forum one developer asked for this.
Bello a simple code sample is given
<TreeView Height="251" HorizontalAlignment="Left" Margin="45,30,0,0"
Name="treeView1" VerticalAlignment="Top" Width="197">
<TreeViewItem Header="Yahoo" IsManipulationEnabled="False" Focusable="False">
<TreeViewItem Header="d" />
<TreeViewItem Header="c" />
<TreeViewItem Header="b" />
<TreeViewItem Header="A" />
Hope this will help, Note that if you have some binding with the tree grid and you want to achieve the same as above you might need to use triggers.