docs: public TreeModel.CompressedTree compress() {
  //    Log.info(Sys.RANDF, _tree.toString(new StringBuilder(), Integer.MAX_VALUE).toString());
      int size = _tree.dtreeSize();
      if (_tree instanceof LeafNode) {
        size += 3;
      }
      AutoBuffer ab = new AutoBuffer(size);
      if( _tree instanceof LeafNode)
        ab.put1(0).put2((char)65535);
      _tree.compress(ab);
      assert ab.position() == size: "Actual size doesn't agree calculated size.";
      char _nclass = (char)_data.classes();
      return new TreeModel.CompressedTree(ab.buf(),_nclass,_seed);
    }