Dear @rene,
Thanks for reaching out to the forum! Yes, RDataFrame can be used also to generate data and fill a TTree-based dataset. I’m not sure I grasp the full picture of your case, but there are many ways to fill a jagged-array to a column with RDF. For example, you can take a look at this other post. Let me know if that is enough for your use case or you need anything more.
Cheers,
Vincenzo