*/
  @SuppressWarnings("unchecked")
  public static <E extends @Nullable Object> TreeMultiset<E> create(
      @CheckForNull Comparator<? super E> comparator) {
    return (comparator == null)
        ? new TreeMultiset<E>((Comparator) Ordering.natural())
        : new TreeMultiset<E>(comparator);
  }

  /**
   * Creates an empty multiset containing the given initial elements, sorted according to the

   */
  @SuppressWarnings("unchecked")
  public static <E extends @Nullable Object> TreeMultiset<E> create(
      @CheckForNull Comparator<? super E> comparator) {
    return (comparator == null)
        ? new TreeMultiset<E>((Comparator) Ordering.natural())
        : new TreeMultiset<E>(comparator);
  }

  /**

  LinkedHashMultiset<Object> linkedHashMultiset;
  HashMultiset<Object> hashMultiset;

  // TreeMultiset requires a Comparable element.
  TreeMultiset<Integer> treeMultiset;

  @BeforeExperiment
  void setUp() {
    hashMultiset = HashMultiset.create(size);
    linkedHashMultiset = LinkedHashMultiset.create(size);
    treeMultiset = TreeMultiset.create();

    Random random = new Random();

    int sizeRemaining = size;

  LinkedHashMultiset<Object> linkedHashMultiset;
  HashMultiset<Object> hashMultiset;

  // TreeMultiset requires a Comparable element.
  TreeMultiset<Integer> treeMultiset;

  @BeforeExperiment
  void setUp() {
    hashMultiset = HashMultiset.create(size);
    linkedHashMultiset = LinkedHashMultiset.create(size);
    treeMultiset = TreeMultiset.create();

    Random random = new Random();

    int sizeRemaining = size;

  }

  public void testToString() {
    Multiset<String> ms = TreeMultiset.create();
    ms.add("a", 3);
    ms.add("c", 1);
    ms.add("b", 2);

    assertEquals("[a x 3, b x 2, c]", ms.toString());
  }

  public void testElementSetSortedSetMethods() {
    TreeMultiset<String> ms = TreeMultiset.create();
    ms.add("c", 1);
    ms.add("a", 3);
    ms.add("b", 2);

  }

  public void testToString() {
    Multiset<String> ms = TreeMultiset.create();
    ms.add("a", 3);
    ms.add("c", 1);
    ms.add("b", 2);

    assertEquals("[a x 3, b x 2, c]", ms.toString());
  }

  public void testElementSetSortedSetMethods() {
    TreeMultiset<String> ms = TreeMultiset.create();
    ms.add("c", 1);
    ms.add("a", 3);
    ms.add("b", 2);

    return generateTreeMultiset(freshElement);
  }

  @Generates
  static <E extends Comparable<E>> TreeMultiset<E> generateTreeMultiset(E freshElement) {
    TreeMultiset<E> multiset = TreeMultiset.create();
    multiset.add(freshElement);
    return multiset;
  }

  @Generates

            .withFeatures(
                CollectionSize.ANY,
                CollectionFeature.KNOWN_ORDER,
                CollectionFeature.ALLOWS_NULL_QUERIES)
            .named("Multisets.unmodifiableMultiset[TreeMultiset]")
            .createTestSuite());

    suite.addTest(
        MultisetTestSuiteBuilder.using(unionGenerator())
            .withFeatures(CollectionSize.ANY, CollectionFeature.ALLOWS_NULL_VALUES)

            .withFeatures(
                CollectionSize.ANY,
                CollectionFeature.KNOWN_ORDER,
                CollectionFeature.ALLOWS_NULL_QUERIES)
            .named("Multisets.unmodifiableMultiset[TreeMultiset]")
            .createTestSuite());

    suite.addTest(
        MultisetTestSuiteBuilder.using(unionGenerator())
            .withFeatures(CollectionSize.ANY, CollectionFeature.ALLOWS_NULL_VALUES)

   *
   * <p>Results are undefined if {@code multiset1} and {@code multiset2} are based on different
   * equivalence relations (as {@code HashMultiset} and {@code TreeMultiset} are).
   *
   * @since 14.0
   */
  public static <E extends @Nullable Object> Multiset<E> union(
      final Multiset<? extends E> multiset1, final Multiset<? extends E> multiset2) {