It may sometimes be useful to store particles always under the same label, for instance always as muminus and not as muplus and muminus in the nTuple. This will allow to chain or merge the root files in an easy way afterwards. A simple example may be:

Tuple = DecayTreeTuple("MisID")
Tuple.InputLocations = ["Phys/StdNoPIDsMuons"]
Tuple.Decay = "[mu+]cc"

which takes every particle, assigns it the ID of a muon / antimuon, and saves it in the tuple. The problem here exactly is that the files can't be merged afterwards.

If you have something like

myTuple = DecayTreeTuple("myTuple")

add

myTuple.RevertToPositiveID = True

which will do the job.