public void IsBst()
        {
            if (Root == null)
            {
                Console.WriteLine("Empty tree");
                return;
            }

            @h@bool isbst = true;
            IsBstHelper2(Root, ref isbst);
            if (isbst == true)
            {
                Console.WriteLine("This a Binary Search Tree");
            }
            else
                Console.WriteLine("This is not a Binary Search Tree");
        }

        private void IsBstHelper2(Node node, ref bool isBst)
        {
            if (node == null)
                return;
            if (node.Left != null)
                IsBstHelper2(node.Left, ref isBst);
            if (node.Right != null)
                IsBstHelper2(node.Right, ref isBst);
            if (node.Right != null && node.Right.Data < node.Data)
                    isBst = false;
            if (node.Left != null && node.Left.Data < node.Data)
                    isBst = false;
        }