Problems with the DLangUI TreeWidget

[pezi_pink via Digitalmars-d-learn]

I am having some seemingly basic problems using the TreeWidget 
from DLangUI on Windows.  I posted on the project's gitter 
channel some time ago but did not get any response.

All I am trying to do is add children to the tree's nodes at 
runtime.  The simple code below attempts to add a new node when a 
button is pressed.  As far as I can tell, the node does indeed 
get added, since the new node responds to keyboard events, but it 
does not render.  I have tried everything to get it to render, 
using all the available invalidate/redraw methods, even as far as 
removing and re-adding the control again to its layout, but 
nothing seems to work.  Any advice would be greatly received!

extern (C) int UIAppMain(string[] args) {
   auto window  = Platform.instance.createWindow("DlangUI example 
- HelloWorld", null);
   auto vlayout = new VerticalLayout();
   TreeWidget tree = new TreeWidget("Root");
   TreeItem tree2 = tree.items.newChild("machinesroot", 
"Machines"d, null);
   auto machine0 = tree2.newChild("machine0", "Machine 0"d, null);
   machine0.newChild("machine0stack", "Stack", null);
   auto btn = (new Button("btn1", "Button 1"d));
   btn.click = delegate(Widget src) {
     // this gets added but does not render
     tree2.newChild("machine1", "Machine 1"d, null);
     return true;
   };
   vlayout.addChild(btn);
   vlayout.addChild(tree);
   window.mainWidget = vlayout;
   window.show();
   return Platform.instance.enterMessageLoop();
}

Thanks