public class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
            //自已绘制
            this.treeView1.DrawMode = TreeViewDrawMode.OwnerDrawText;
            this.treeView1.DrawNode+=new DrawTreeNodeEventHandler(treeView1_DrawNode);
        }

        //在绘制节点事件中，按自已想的绘制
        private void treeView1_DrawNode(object sender, DrawTreeNodeEventArgs e)
        {

            if ((e.State & TreeNodeStates.Selected) != 0)
            {
                //演示为绿底白字
                e.Graphics.FillRectangle(Brushes.Green,e.Node.Bounds);

                Font nodeFont = e.Node.NodeFont;
                if (nodeFont == null) nodeFont = ((TreeView)sender).Font;

 
                e.Graphics.DrawString(e.Node.Text, nodeFont, Brushes.White,
                    Rectangle.Inflate(e.Bounds, 2, 0));
            }
            else
            {
                e.DrawDefault = true;
            }

            if ((e.State & TreeNodeStates.Focused) != 0)
            {
                using (Pen focusPen = new Pen(Color.Black))
                {
                    focusPen.DashStyle = System.Drawing.Drawing2D.DashStyle.Dot;
                    Rectangle focusBounds = e.Node.Bounds ;
                    focusBounds.Size = new Size(focusBounds.Width - 1,
                    focusBounds.Height - 1);
                    e.Graphics.DrawRectangle(focusPen, focusBounds);
                }
            }

        }
    }

------解决方案--------------------
给你个遮盖的方法把


   private void treeView1_AfterSelect(object sender, TreeViewEventArgs e)
       {
           TreeView _TreeView = (TreeView)sender;
           Control _SetLabel = _TreeView.Controls["SelectLab"];
           if (_SetLabel == null)
           {
               Label _Label = new Label();
               _Label.Name = "SelectLab";
               _Label.AutoSize = false;
               _Label.BackColor = Color.Yellow;
               _Label.ForeColor = Color.Red;
               _Label.Font = _TreeView.Font;
               _TreeView.Controls.Add(_Label);
               _SetLabel = _Label;
           }
           _SetLabel.Size = new Size(e.Node.Bounds.Width + 5, e.Node.Bounds.Height);
           _SetLabel.Location = new Point(e.Node.Bounds.X, e.Node.Bounds.Y);
           _SetLabel.Text = e.Node.Text;
       }