presto-main/src/main/java/io/prestosql/operator/ExplainAnalyzeOperator.java/ExplainAnalyzeOperator/getSubStagesOf
class ExplainAnalyzeOperator:    private static List<StageInfo> getSubStagesOf(StageId stageId, StageInfo rootStage)
    {
        ImmutableList.Builder<StageInfo> collector = ImmutableList.builder();
        getSubStages(stageId, rootStage, collector, false);
        return collector.build();
    }