private void TreeView_DoubleClick(object sender, EventArgs e)
        {
            if (this.TreeView.SelectedNode != null)
            {
                if (this.TreeView.SelectedNode.IsExpanded)
                {
                    this.TreeView.SelectedNode.Collapse();
                }
                else
                {
                    this.TreeView.SelectedNode.Expand();
                }
            }
        }