TreeNode curNode;
private void treeView1_AfterSelect(object sender, TreeViewEventArgs e)
{
    curNode = e.Node;
    this.textBox1.Text = e.Node.Text;
}
private void button1_Click(object sender, EventArgs e)
{
    curNode.Text = this.textBox1.Text;
}

------解决方案--------------------
js可以解决，麻烦些

------解决方案--------------------
private void treeView1_AfterSelect(object sender, TreeViewEventArgs e)  
{  
   this.textBox1.Text = e.Node.Text;  
}  
在Button的Clieck事件中
if(this.treeView1.SelectedNode!=null)
			{
				if(this.textBox2.Text !=this.treeView1.SelectedNode.Text)
				{
					this.treeView1.SelectedNode.Text = this.textBox2.Text;
				}
			}

随便设置下TreeView的HideSelection =false;