how to check name of treeview nodes is same or not any other nodes in c#

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;

namespace Test_TreeView
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
            this.Load += Form1_Load;
        }

        void Form1_Load(object sender, EventArgs e)
        {
            this.RenameNode("Node7", "Node6");

        }

        void RenameNode(string oldt, string newt)
        {
            // if new text exists return
            if (CheckNodeText(this.treeView1.TopNode, newt))
                return;
            // if node found, rename it
            TreeNode n = FindNode(this.treeView1.TopNode, oldt);
            if (n != null)
                n.Text = newt;
        }

        // check text if exists
        bool CheckNodeText(TreeNode node, string text)
        {
            if (node.Text == text)
                return true;
            for (int i = 0; i < node.Nodes.Count; i++)
            {
                if (CheckNodeText(node.Nodes[i], text))
                    return true;
            }
            return false;
        }

        // find the node having text
        TreeNode FindNode(TreeNode node, string text)
        {
            if (node.Text == text)
                return node;
            for (int i = 0; i < node.Nodes.Count; i++)
            {
                TreeNode n = FindNode(node.Nodes[i], text);
                if (n != null)
                    return n;
            }
            return null;
        }

    }
}