The RadTreeView allows you to enable connected lines between the nodes of a treeview. By default the connecting lines between the nodes are not enabled (they are not visible). You should use a single property to do so - IsLineEnabled and set it to True.
<telerik:RadTreeView x:Name="radTreeView" IsLineEnabled="True">
|For more information about the visual structure of the RadTreeView, check out the Visual Structure topic.|
Change the LineColor