private TreeMultiset(
      Reference<AvlNode<E>> rootReference, GeneralRange<E> range, AvlNode<E> endLink) {
    super(range.comparator());
    this.rootReference = rootReference;
    this.range = range;
    this.header = endLink;
  }

  private TreeMultiset(Comparator<? super E> comparator) {
    super(comparator);
    this.range = GeneralRange.all(comparator);
    this.header = new AvlNode<>();