As your question is not that much clear to give you a proper solution still i am trying here to give you some choices to get the solution or a hint to your solution.
Let say my TreeView name is 'tvTest'. Now the design for it is :-
<asp:treeview runat="server" id="tvTest" xmlns:asp="#unknown">
<nodes>
<asp:treenode text="Item 1">
<asp:treenode text="Item 1.1"></asp:treenode>
<asp:treenode text="Item 1.2"></asp:treenode>
<asp:treenode text="Item 1.3"></asp:treenode>
</asp:treenode>
<asp:treenode text="Item 2">
<asp:treenode text="Item 2.1"></asp:treenode>
<asp:treenode text="Item 2.2"></asp:treenode>
</asp:treenode>
<asp:treenode text="Item 3">
<asp:treenode text="Item 3.1"></asp:treenode>
</asp:treenode>
</nodes>
</asp:treeview>
To get SelectedNode value only we can go by two ways like :-
tvTest.SelectedValue
tvTest.SelectedNode.Value
To get the selected node text :-
tvTest.SelectedNode.Text
To get the path for the values from parent to current :-
tvTest.SelectedNode.ValuePath
Hope this will be of help to you.
Please let me know if you need help on any other way ?