public static void Main(string [] args)
{
Tree <int> T1 = new Tree <int>(1, null, null);
Tree <int> T2 = new Tree <int>(3, null, null);
Tree <int> T3 = new Tree <int>(5, null, null);
Tree <int> T4 = new Tree <int>(7, null, null);
Tree <int> T5 = new Tree <int>(2, T1, T2);
Tree <int> T6 = new Tree <int>(6, T3, T4);
Tree <int> T7 = new Tree <int>(4, T5, T6);
TreeIterator t = new TreeIterator();
t.display(T7);
}