code: private ParseTree parseRelational(Expression expressionIn) {
      SourcePosition start = getTreeStartLocation();
      ParseTree left = parseShiftExpression();
      while (peekRelationalOperator(expressionIn)) {
        Token operator = nextToken();
        ParseTree right = parseShiftExpression();
        left = new BinaryOperatorTree(getTreeLocation(start), left, operator, right);
      }
      return left;
    }
docs: 11.8 Relational