Resizing a tree view

Dear friends,

My script finally shall create a tree view displaying the heading-structure of a document.
One detail is that window and tree should be resizeable.
It's easy to resize the window, but for the tree to adapt to the new space I have no success.
It's also a question to me, why the OnResiz is triggered before I touch the created window.

Do You have any ideas where I need to change?

Klaus

/* TreeViewResize.jsx ====== UTF-8 =========================================
              Create a tree contents and experiment with resizing
Refrence      C:\Program Files (x86)\Adobe\Adobe Utilities - CS6\ExtendScript Toolkit CS6\SDK\Samples\javascript\SnpCreateTreeView.jsx
              Rick Quatro's DocNav.jsx
*/
main ();

function main () {
	var j, k, oTree, wViewTree;

  wViewTree = new Window("palette", "Static (generated) tree", undefined, {resizeable: true});

	oTree = wViewTree.add("treeview");
// oTree.preferredSize = [300, 200];
	for(var j = 0;j < 10;j++)	{        // Add static items to the list, in a hierarchical structure.
		oTree.add("node", "Item " + j);	
		for(k = 0; k < 4; k++) {
			oTree.items[j].add("item", "Sub Item " + k);
		}
	}
// --- behaviour of the window -------------------
  wViewTree.onResize = Resize (wViewTree, oTree);
// --- final actions -----------------------------
  ExpandNode(oTree);
  wViewTree.show();
} // end of main

function Resize (wViewTree, oTree) { // Resize window and tree =============
var wSize;
  wViewTree.layout.resize (); 
  alert ("Why is this entered  before I do a resize?");
/* --- this poart does not work at all 
  wSize = wViewTree.preferredSize;
$.bp(true);
//oTree.minimumSize = [wSize[0]-30, wSize[1]-30];
  wViewTree.show();
*/
} // end of Resize

function ExpandNode (tree){ // Expand all nodes to see the tree ============
  tree.expanded = true;
  var branches = tree.items;
  for (var i = 0; i < branches.length; i++) {
    if (branches[i].type == 'node') {
      ExpandNode (branches[i]);
    }
  }
} // end of ExpandNode