code: @Override public int compare(WBSType o1, WBSType o2)
     {
        Integer parent1 = o1.getParentObjectId();
        Integer parent2 = o2.getParentObjectId();
        int result = NumberHelper.compare(parent1, parent2);
        if (result == 0)
        {
           Integer seq1 = o1.getSequenceNumber();
           Integer seq2 = o2.getSequenceNumber();
           result = NumberHelper.compare(seq1, seq2);
        }
        return result;
     }
docs: {@inheritDoc}