A screenhot clearly indicating the initial and expected lists could be useful. You can check first what’s already available on this topic and start to experiment from that, see for example:
- http://dynamoprimer.com/en/06_Designing-with-Lists/6-3_lists-of-lists.html
- Dynamo Dictionary
- Enjoy Revit: Examples for All List Actions in DYNAMO
- Managing Lists in Dynamo – landarchBIM
- See also if existing discussions can’t help, such as this one for instance: