code: public Set<SortedSet<T>> allSupersets(final SortedSet<T> set) {
          final Set<SortedSet<T>> supersets = new LinkedHashSet<>();
          allSupersets(set, this.rootNodes, supersets);
          return supersets;
      }
docs: Returns all supersets of a given set in this UBTree.
  @param set the set to search for
  @return all supersets of the given set