Group By Parent Span

In Lightstep Cloud Observability when looking at operations in aggregate, how can I group by the parent operation span name?

My use case is I have two operations, let's call them parent_1 and parent_2. Both of them always have a child operation span within them. The parent operations have side effects that can impact the latency of the child operation. I want to see the average P50 for the child operations, grouped by the parent operation.

Lightstep seemingly already understands parent-child relationships, which I can view in the Dependency Map. But it doesn't show me aggregated latencies there.

I can add metadata to the child spans, but this feels wasteful in terms of data costs and requiring additional code.