Binary search tree - Post-order Traversal, C#

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//Rextester.Program.Main is the entry point for your code. Don't change it.
//Compiler version 4.0.30319.17929 for Microsoft (R) .NET Framework 4.5

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text.RegularExpressions;

namespace Rextester
{
    public class Program
    {
        public static void Main(string[] args)
        {
            
            // Post-order Traversal - The root node is visited last. First we traverse the left subtree, then the right subtree and finally the root node.
            
            //Your code goes here
            Console.WriteLine("Hello, world!");
            Tree bsTree = new Tree();
            bsTree.Insert(2);
            bsTree.Insert(4);
            bsTree.Insert(6);
            bsTree.Insert(8);
            bsTree.Insert(10);
            bsTree.Insert(12);
            bsTree.Insert(1);
            bsTree.Insert(3);
            bsTree.Insert(5);
            bsTree.Insert(7);
            bsTree.Insert(9);
            bsTree.Insert(11);
            
            Console.WriteLine("Preorder Traversal : ");
            bsTree.Postorder(bsTree.ReturnRoot());
            Console.WriteLine(" ");
            Console.WriteLine();
            
        }
    }
    
     class Node  {
        public int item;
        public Node left;
        public Node right;
        public void display()
        {
            Console.Write(" ");
            Console.Write(item);
            Console.Write(" ");
        }
    }
    
    class Tree
    {
        public Node root;
        public Tree()
        {
            root = null;
        }
        public Node ReturnRoot()
        {
            return root;
        }
        public void Insert(int id)
        {
            Node newNode = new Node();
            newNode.item = id;
            if (root == null)
                root = newNode;
            else
            {
                Node tempNode = root;
              
                while (true)
                {
                    if (id < tempNode.item)
                    {
                        if (tempNode.left == null)
                        {
                            tempNode.left = newNode;
                            return;
                        }
                        tempNode = tempNode.left;
                    }
                    else
                    {
                        if (tempNode.right == null)
                        {
                            tempNode.right = newNode;
                            return;
                        }
                        tempNode = tempNode.right;
                    }
                }
            }
        }
      
        public void Postorder(Node Root)
        {
            if (Root != null)
            {
                Postorder(Root.left);
                Postorder(Root.right);
                Root.display();
            }
        }
       
    }
    
}

Show compiler warnings [ + ] Show input
Compilation time: 0,14 sec, absolute running time: 0,13 sec, cpu time: 0,11 sec, average memory usage: 13 Mb, average nr of threads: 2, absolute service time: 0,3 sec