presto-main/src/main/java/io/prestosql/util/GraphvizPrinter.java/GraphvizPrinter/visitGroupId
class GraphvizPrinter:        @Override
        public Void visitGroupId(GroupIdNode node, Void context)
        {
            // grouping sets are easier to understand in terms of inputs
            List<String> inputGroupingSetSymbols = node.getGroupingSets().stream()
                    .map(set -> "(" + Joiner.on(", ").join(set.stream()
                            .map(symbol -> node.getGroupingColumns().get(symbol))
                            .collect(Collectors.toList())) + ")")
                    .collect(Collectors.toList());

            printNode(node, "GroupId", Joiner.on(", ").join(inputGroupingSetSymbols), NODE_COLORS.get(NodeType.AGGREGATE));
            return node.getSource().accept(this, context);
        }