@Override
    public IntervalNode<T> getPrevSibling(@NotNull IntervalNode<T> element) {
      IntervalNode<T> parent = element.getParent();
      if (parent == null) return null;
      return parent.getRight() == element ? parent.getLeft() : null;
    }
@Override
    public IntervalNode<T> getPrevSibling(@NotNull IntervalNode<T> element)