}
      };
    }

    /** Uses a naturally-ordered {@link TreeSet} to store value collections. */
    @SuppressWarnings("rawtypes")
    public SortedSetMultimapBuilder<K0, Comparable> treeSetValues() {
      return treeSetValues(Ordering.natural());
    }

    /**
     * Uses a {@link TreeSet} ordered by the specified comparator to store value collections.
     *