要实现这种功能，必须重新绘制树节点（tree node）。我们可以设置TreeView.DrawMode属性为OwnerDrawAll并处理DrawNode事件。请参考以下代码：
代码：
private void treeView_DrawNode(object sender, DrawTreeNodeEventArgs e)
{
if (IsThirdLevel(e.Node))
{
Color backColor, foreColor;
if ((e.State & TreeNodeStates.Selected) == TreeNodeStates.Selected)
{
backColor = SystemColors.Highlight;
foreColor = SystemColors.HighlightText;
}
else if ((e.State & TreeNodeStates.Hot) == TreeNodeStates.Hot)
{
backColor = SystemColors.HotTrack;
foreColor = SystemColors.HighlightText;
}
else
{
backColor = e.Node.BackColor;
foreColor = e.Node.ForeColor;
}
using (SolidBrush brush = new SolidBrush(backColor))
{
e.Graphics.FillRectangle(brush, e.Node.Bounds);
}
TextRenderer.DrawText(e.Graphics, e.Node.Text, this.treeView.Font, e.Node.Bounds, foreColor, backColor);
if ((e.State & TreeNodeStates.Focused) == TreeNodeStates.Focused)
{
ControlPaint.DrawFocusRectangle(e.Graphics, e.Node.Bounds,
foreColor, backColor);
}
e.DrawDefault = false;
}
else
{
e.DrawDefault = true;
}
}
