I'm trying to do a similar thing, and I'm using the 2015.1.401.40 version. Unfortunately I keep getting the javscript error "Object doesn't support property or method 'get_text'". The top of the call stack being here (in the minimized code):
The reason seems to be that it keeps calling get_parent until it's null but that finds the radtreeview and it doesn't have a get_text function on it. I tried to get around this by calling _createEntry directly with a disconnected node but that doesn't work at all (though it doesn't give the error as it doesn't have a parent without a get_text function.
Is there a better way to, client side, select a node and add it as an entry with the latest version?