public void EachPostOrder(Action <T> action)
 {
     LeftChild?.EachPostOrder(action);
     RightChild?.EachPostOrder(action);
     action.Invoke(this.Value);
 }
 public void EachPostOrder(Action <T> action)
 {
     LeftChild?.EachPostOrder(action);
     RightChild?.EachPostOrder(action);
     action(Value);
 }