TreeView - get all selected (checkbox) nodes on button click

I have a treeview control with checkboxes that I need to get the unique identifier value of all checked nodes on a button click.  I dont need the control to update until the user actually clicks the button.  A stored procedure generates a datatable with the following structure.

SportID        SportName      LeagueID        League
------------------------------------------------------------------
101               Basketball        400              1st Grade
101               Basketball        401              2nd Grade
102               Volleyball         650               Girls Red Div
etc.

The Treeview is build the tree using the code below.  

The Treeview displays SportName and League, but the value that I need to retrieve is the LeagueID.  Once the user clicks the button, I need a list of all the checked LeagueIDs.  In a datagrid I would do something like
For n as integer = 0 to Datagrid.Rows.Count -1
       If Datagrid.Rows(n).Cells(5).Value = true then
               LeagueID = Datagrid.Rows(n).Cells("LeagueID").value
               stringbuilder or something with LeagueID
       end if
Next.  

But I can't seem to find a similar method to work with the treeview.

Thanks,
Clint...

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