Same branches in different trees

I would like to know how can I join the content of a certain branch obtained in multiple trees (I wanted to obtain a certain result from a Monte Carlo simulation, by running many times the same program with a different seed).
thanks a lot,

I did it with TChain,
thanks anyway!

Once I created the TChain, I try to write the results of the chain in another tree. Why do I obtain two trees of approximately half of the results each?

“how” did you write the result?
Most likely you need to increase the default file size limit. See … axTreeSize:mytree->SetMaxTreeSize(1900000000000LL);