presto-parser/src/main/java/io/prestosql/sql/parser/AstBuilder.java/AstBuilder/visitMultipleGroupingSets
class AstBuilder:    @Override
    public Node visitMultipleGroupingSets(SqlBaseParser.MultipleGroupingSetsContext context)
    {
        return new GroupingSets(getLocation(context), context.groupingSet().stream()
                .map(groupingSet -> visit(groupingSet.expression(), Expression.class))
                .collect(toList()));
    }