Thank you for trying out the TreeListView.
With the TreeListView you can register for the Click routed event like so:
Then in the handler you can check for the click count:
sender, ClickEventArgs e)
(e.ClickCount == 2)
Please note that the TreeList is still a CTP and this code may be subject to change.
Also to see the .AddHandler method you need to have the Telerik.Windows
the Telerik team