Steps: - Take a windows form and drag drop a TreeView Control and write code which is given below

Code:-

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
 
namespace TreeViewDragDrop
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
            TreeNode rootNode = treeView1.Nodes.Add("USA");
 
            // Create the Child nodes for the root
            TreeNode states1 = rootNode.Nodes.Add("New York");
            TreeNode states2 = rootNode.Nodes.Add("Michigan");
            TreeNode states3 = rootNode.Nodes.Add("Wisconsin");
            TreeNode states4 = rootNode.Nodes.Add("California");
 
            // Create siblings nodes for the Child nodes
            TreeNode child = states1.Nodes.Add("Rochester");
            child = states1.Nodes.Add("New York");
            child = states1.Nodes.Add("Albany");
            child = states2.Nodes.Add("Detroit");
            child = states2.Nodes.Add("Ann Arbor");
            child = states2.Nodes.Add("Lansing");
            child = states3.Nodes.Add("Milwaukee");
            child = states3.Nodes.Add("Madison");
            child = states3.Nodes.Add("La Cross");
            child = states4.Nodes.Add("Los Angeles");
            child = states4.Nodes.Add("San Fransisco");
            child = states4.Nodes.Add("San Diego");
 
            // Expand all tree nodes when first loaded
            treeView1.AllowDrop = true;
            treeView1.ExpandAll();
 
 
        }
 
        private void Form1_Load(object sender, EventArgs e)
        {
        }
 
        private void treeView1_DragEnter(object sender, DragEventArgs e)
        {
            e.Effect = DragDropEffects.Move;
        }
 
        private void treeView1_DragDrop(object sender, DragEventArgs e)
        {
            TreeNode SourceNode = (TreeNode)e.Data.GetData("System.Windows.Forms.TreeNode");
            Point pt = ((TreeView)sender).PointToClient(new Point(e.X, e.Y));
            TreeNode DestinationNode = ((TreeView)sender).GetNodeAt(pt);
           
            try
            {
                int sourceIndex = SourceNode.Index;
                int destIndex = DestinationNode.Index;
 
                if (SourceNode.Level == 1 && DestinationNode.Level == 1)
                {
                    if (sourceIndex < destIndex)
                    {
                        TreeNode parentNode = SourceNode.Parent;
                        SourceNode.Remove();
                        DestinationNode.Remove();
                        parentNode.Nodes.Insert(sourceIndex, DestinationNode);
                        parentNode.Nodes.Insert(destIndex, SourceNode);
                    }
                    else
                    {
                        TreeNode parentNode = SourceNode.Parent;
                        SourceNode.Remove();
                        DestinationNode.Remove();
                        parentNode.Nodes.Insert(sourceIndex - 1, DestinationNode);
                        parentNode.Nodes.Insert(destIndex, SourceNode);
                    }
                }
 
                else if (SourceNode.Level == 2 && DestinationNode.Level == 2)
                {
                   
                    if (SourceNode.Parent == DestinationNode.Parent)
                    {
                        if (sourceIndex < destIndex)
                        {
                            TreeNode parentNode = SourceNode.Parent;
                            SourceNode.Remove();
                            DestinationNode.Remove();
                            parentNode.Nodes.Insert(sourceIndex, DestinationNode);
                            parentNode.Nodes.Insert(destIndex, SourceNode);
                        }
                        else
                        {
                            TreeNode parentNode = SourceNode.Parent;
                            SourceNode.Remove();
                            DestinationNode.Remove();
                            parentNode.Nodes.Insert(sourceIndex - 1, DestinationNode);
                            parentNode.Nodes.Insert(destIndex, SourceNode);
                        }
                    }
                    else
                    {
                        TreeNode addNode = DestinationNode.Parent;
                        SourceNode.Remove();
                        addNode.Nodes.Insert(destIndex, SourceNode);
                       
                    }
                }
 
                else if (SourceNode.Level == 2 && DestinationNode.Level == 1)
                { 
                    if (DestinationNode.Nodes.Count==0)
                    {
                        SourceNode.Remove();
                        DestinationNode.Nodes.Insert(0, SourceNode);               
                    }
                    else
                    {
                        int i = DestinationNode.LastNode.Index;
                        SourceNode.Remove();
                        DestinationNode.Nodes.Insert(i + 1, SourceNode);
                    }
                }
            }
            catch
            {
                MessageBox.Show("Drag on node...");
            }
        }
 
        private void treeView1_ItemDrag(object sender, ItemDragEventArgs e)
        {
            DoDragDrop(e.Item, DragDropEffects.Move);
        }
 
 
        private void treeView1_AfterSelect(object sender, TreeViewEventArgs e)
        {
 
        }
    }
}

 Output:-