private void UpdateTree()
        {
            this.InvokeLater(() =>
            {
                SelectionTree.BeginUpdate();

                SelectionTree.Nodes.Clear();

                var doc = _context.Get <MapDocument>("ActiveDocument");
                if (doc != null)
                {
                    foreach (var root in doc.Selection.GetSelectedParents())
                    {
                        SelectionTree.Nodes.Add(CreateNode(root));
                    }
                }

                SelectionTree.ExpandAll();
                SelectionTree.EndUpdate();
            });
        }