get a list of treeview selected node children

Hi, i want get a list or array of values of treeview selected node all children in each level.
for example: if i select programming node > string[] nodes = new string[] {"programming", "web", "asp.net","php","application","c#","Java"};
-network
-programing
--web
---asp.net
---php
--application
---c#
---Java