docs: public static long depth_leaves( AutoBuffer tbits, boolean regression ) {
      return new TreeVisitor<RuntimeException>(tbits, regression) {
        int _maxdepth, _depth, _leaves;
        @Override protected TreeVisitor leafFloat(float fl) { _leaves++; if(_depth > _maxdepth) _maxdepth = _depth; return this; }
        @Override protected TreeVisitor leaf(int tclass ) { _leaves++; if( _depth > _maxdepth ) _maxdepth = _depth; return this; }
        @Override protected TreeVisitor pre (int col, float fcmp, int off0, int offl, int offr ) { _depth++; return this; }
        @Override protected TreeVisitor post(int col, float fcmp ) { _depth--; return this; }
        @Override long result( ) {return ((long)_maxdepth<<32) | _leaves; }
      }.visit().result();
    }