public static string TreePostorderIteratorTest(int[] array)
        {
            string s = "";

            Tree<int> tree = new Tree<int>(array[0]);

            for (int a = 1; a < array.Length; a++)
                tree.AddNode(array[a]);

            foreach (int a in tree.PostorderIterator())
                s += a;

            Debug.WriteLine(s);

            return s;
        }