presto-parser/src/main/java/io/prestosql/sql/parser/AstBuilder.java/AstBuilder/visitSingleGroupingSet
class AstBuilder:    @Override
    public Node visitSingleGroupingSet(SqlBaseParser.SingleGroupingSetContext context)
    {
        return new SimpleGroupBy(getLocation(context), visit(context.groupingSet().expression(), Expression.class));
    }