code: public void add(final ITreeData paramNodeX, final ITreeData paramNodeY) throws TTIOException {
          mMapping.put(paramNodeX, paramNodeY);
          mReverseMapping.put(paramNodeY, paramNodeX);
          updateSubtreeMap(paramNodeX, mRtxNew);
          updateSubtreeMap(paramNodeY, mRtxOld);
      }
docs: Adds the matching x -> y.
  
  @param paramNodeX
  source node
  @param paramNodeY
  partner of paramNodeX
  @throws TTIOException