You're close! The Add method will return a reference to the node. See additions to your code in bold. I'm not sure if that will work because the node you just created doesn't contain any children, but I haven't ran into that situation before.

Select CurNodes
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   <b>oNewNode = </b>ThisForm.trvTreeView.Nodes.Add (cRelative, 4, cNodeKey, cText, nImage)

   If cNodeType = "s"
      <b>oNewNode.Expanded = .T.</b>
   endif

   .....

EndScan

ThisForm.trvTreeView.Nodes (1).Expanded = .T.