static <B> MultiSetMap<S, B> ciMultiSetMap_innerTreeSet(Comparator<B> innerComparator default null) {
  MultiSetMap<S, B> mm = new MultiSetMap<S, B>() {
    Set<B> _makeEmptySet() { ret new TreeSet(innerComparator); }
  };
  mm.data = ciMap();
  ret mm;
}