That's how we do it - there are "branches" to most of our RCAs, and in fact, we have separate sections for root cause analysis (things which directly or indirectly contribute to incident, which are a branched / fractal 5 whys) and lessons learned (things which did not necessarily contribute to incident but which upon reflection we can do better - frequently incident management or communication or reporting or escalation etc).

It took a while for all the teams to embrace the rca process without fear and finger pointing, but now that it's trusted and accepted, problem management stream / rca process probably the healthiest / best viewed of our streams and processes :-)