private void treeView1_AfterLabelEdit(object sender, NodeLabelEditEventArgs e)
{
     Items[e.Node.Parent.Index][e.Node.Index] = e.Node.Text;
}

                string beforeEdit = "";
                string afterEdit = "";

        private void treeView3_BeforeLabelEdit(object sender, NodeLabelEditEventArgs e)
        {
            BeforeTreeEdit(treeView3, sender, e);
        }
        private void treeView3_AfterLabelEdit(object sender, NodeLabelEditEventArgs e)
        {
            AfterTreeEdit(treeView3, sender, e);
        }

        private void BeforeTreeEdit(TreeView Tree, object sender, NodeLabelEditEventArgs e)
        {
            // Determine whether the user has selected the top node. If so,
            // change the LabelEdit property to false so the user cannot
            // edit this label.
            if (e.Node == Tree.TopNode)
            {
                Tree.LabelEdit = false;
                MessageBox.Show("You are not allowed to edit the top node", "Illegal Node", MessageBoxButtons.OK);
            }
            // Allow the user to edit only the Value node
            else if (e.Node.Level < 2)
            {
                Tree.LabelEdit = false;
                MessageBox.Show("This node cannot be edited", "Illegal Node", MessageBoxButtons.OK);
            }
            Tree.LabelEdit = true;
            beforeEdit = e.Node.ToString();
        }
        private void AfterTreeEdit(TreeView Tree, object sender, NodeLabelEditEventArgs e)
        {
            afterEdit = e.Label;
            if (beforeEdit != afterEdit && afterEdit != null)
            {
                e.Node.BackColor = Color.Yellow;
            }
        }