code: @Override
      public boolean containsInstance(int value, T instance) {
      	if (root == null) return false;
      	if (value < first.value) return false;
      	if (value > last.value) return false;
      	if (value == first.value && instance == first.element) return true;
      	if (value == last.value && instance == last.element) return true;
      	return containsInstance(root, value, instance);
      }
docs: Returns true if the given key exists in the tree and its associated value is the given element.
  Comparison of the element is using the == operator.