private void treeView1_NodeMouseClick(object sender, TreeNodeMouseClickEventArgs e)

        {

            if (e.Button == MouseButtons.Left)

            {

                    if (!e.Node.IsExpanded & treeView1.HitTest(e.X, e.Y).Location != TreeViewHitTestLocations.PlusMinus)

                    {

                        e.Node.Expand();

                    }

            }

 

        }