code: private void addLeafLabel() {
          final int nodeKind = mRtx.getNode().getKind();
          if (!mLeafLabels.containsKey(nodeKind)) {
              mLeafLabels.put(nodeKind, new ArrayList<ITreeData>());
          }
          mLeafLabels.get(nodeKind).add(mRtx.getNode());
      }
docs: Add leaf node label.