code: private void batch_insert(Collection<Integer> set, boolean parallel)
      {
          for(int i : set)
              store[size++] = i;
          if(parallel)
              Arrays.parallelSort(store, 0, size);
          else
              Arrays.sort(store, 0, size);
      }
docs: more efficient insertion of many items by placing them all into the
  backing store, and then doing one large sort.
  
  @param set
  @param parallel