code: public int compareTo(final OMVRBTreeEntry<K, V> o) {
      if (o == null)
        return 1;
      if (o == this)
        return 0;
      if (getSize() == 0)
        return -1;
      if (o.getSize() == 0)
        return 1;
      if (tree.comparator != null)
        return tree.comparator.compare(getFirstKey(), o.getFirstKey());
  
      return ((Comparable<K>) getFirstKey()).compareTo(o.getFirstKey());
    }
docs: Compares two nodes by their first keys.