BST logic error ... incorrect results

I made this code using Mark Gravell in

Why can't I find _left and _right in BinarySearchTree?
& Amp;
How to fix implicit conversion error in BST C # code?

its a binary search tree, but now I have a boolean error. The results that come up are wrong, the output of my code is as follows:

2
3
5
6
10
17
------------------------------------------------
17
2
------------------------------------------------
3                 
6
Press any key to continue . . .

      

        
        
        
      

    

the last two numbers should give a total of 6 items inserted, but its display is 9

but the way How can I get the height of the tree ?!

using System;
using System.Collections.Generic;
using System.Text;

namespace errors
{
    class Program
    {
        static void Main(string[] args)
        {
            BinarySearchTree t = new BinarySearchTree();

            t.insert(ref t.root, 10);
            t.insert(ref t.root, 5);
            t.insert(ref t.root, 6);
            t.insert(ref t.root, 17);
            t.insert(ref t.root, 2);
            t.insert(ref t.root, 3);

            BinarySearchTree.print(t.root);

            Console.WriteLine("------------------------------------------------");
            Console.WriteLine(t.FindMax());
            Console.WriteLine(t.FindMin());
            Console.WriteLine("------------------------------------------------");

            Console.WriteLine(t.CountLeaves(t.root));
            Console.WriteLine(t.CountNodes(t.root));

        }

        public class TreeNode
        {
            public int n;
            public TreeNode _left;
            public TreeNode _right;


            public TreeNode(int n, TreeNode _left, TreeNode _right)
            {
                this.n = n;
                this._left = _left;
                this._right = _right;
            }


            public void DisplayNode()
            {
                Console.Write(n);
            }


        }


        public class BinarySearchTree
        {
            public TreeNode root;


            public BinarySearchTree()
            {
                root = null;
            }


            public void insert(ref TreeNode root, int x)
            {
                if (root == null)
                {
                    root = new TreeNode(x, null, null);
                }
                else
                    if (x < root.n)
                        insert(ref root._left, x);
                    else
                        insert(ref root._right, x);
            }

            public int FindMin()
            {
                TreeNode current = root;

                while (current._left != null)
                    current = current._left;

                return current.n;
            }

            public int FindMax()
            {
                TreeNode current = root;

                while (current._right != null)
                    current = current._right;

                return current.n;
            }



            public TreeNode Find(int key)
            {
                TreeNode current = root;

                while (current.n != key)
                {
                    if (key < current.n)
                        current = current._left;
                    else
                        current = current._right;
                    if (current == null)
                        return null;
                }
                return current;
            }



            public void InOrder(ref TreeNode root)
            {
                if (root != null)
                {
                    InOrder(ref root._left);
                    root.DisplayNode();
                    InOrder(ref root._right);
                }
            }

            public int CountNodes(TreeNode root)
            {
                int count=1;
                if (root._left != null)
                    count += CountNodes(root._left);
                if (root._right != null)
                    count += CountNodes(root._right);
                return count;
            }

            public int CountLeaves(TreeNode root)
            {
                int count = (root._left == null && root._right == null) ? 1 : 0;
                if (root._left != null)
                    count += CountLeaves(root._left);
                if (root._right != null)
                    count += CountLeaves(root._right);
                return count;
            }


            public static void print(TreeNode root)
            {
                if (root != null)
                {
                    print(root._left);
                    Console.WriteLine(root.n.ToString());
                    print(root._right);
                }

            }



        }

    }
}

      

        
        
        
      

    

Thanx in advance and special thanx for Mark Gravell.