private DateTime treeViewUsers_lastClick = DateTime.Now;
        private void treeViewUsers_MouseLeftButtonUp(object sender, MouseButtonEventArgs e)
        {
            if (((DateTime.Now - treeViewUsers_lastClick).Ticks < 2500000) && (sender!=null))
            {
                TreeViewItem treeViewItem = (sender as TreeView).SelectedItem as TreeViewItem;
                DoubleClickOperation(treeViewItem);             
            }
            treeViewUsers_lastClick = DateTime.Now;
        }

    public class MyTreeView : TreeView
    {
        protected override void OnMouseLeftButtonUp(MouseButtonEventArgs e)
        {            
            ??? O_o
            base.OnMouseLeftButtonUp(e);
        }
    }