RE: Tree is created but never displayed !

I did not look at the code more than a few seconds (maybe someone else can), but I suspect a layout problem (different components have different default sizes). Try to add “?debug” to your URL and then click the “Analyze layouts” button.

You could also use e.g. Firebug or the developer tools in whatever browser you are using to check that the tree is there but so small as to be invisible.