code: @Override
      public void addWordToIndex(int index, String label) {
          if (index >= 0) {
              T token = tokenFor(label);
              if (token != null) {
                  idxMap.put(index, token);
                  token.setIndex(index);
              }
          }
      }
docs: This method allows to insert specified label to specified Huffman tree position.
  CAUTION: Never use this, unless you 100% sure what are you doing.
  
  @param index
  @param label