Separate option for mcPaths TreeName

From email:

For a while we've been using the 'mcPaths' config option for defining our input files, with a format like:

mcPaths: /eos/atlas/atlascerngroupdisk/phys-higgs/HSG6/Htautau/lephad/190116/mc/mc16a/nom/:NOMINAL

And when attempting to loop through systematic tree variations (!=NOMINAL), we parse through a Python script a command option like:

prepare.py -options mcPaths=PATH+':'+TREE

(Yes, unfortunately we are still using an older method for systematics calculation)
Nowadays, things have changed with the introduction of the campaign manager configs, which have been really useful across the whole code.
However, this means we now have to define mcPaths multiple times for each campaign within this other type of config file.

[c16a]
mcPaths: /eos/atlas/atlascerngroupdisk/phys-higgs/HSG6/Htautau/lephad/190116/mc/mc16a/nom/:NOMINAL
[c16d]
mcPaths: /eos/atlas/atlascerngroupdisk/phys-higgs/HSG6/Htautau/lephad/190116/mc/mc16d/nom/:NOMINAL
[c16e]
mcPaths: /eos/atlas/atlascerngroupdisk/phys-higgs/HSG6/Htautau/lephad/190116/mc/mc16e/nom/:NOMINAL

Thus it doesn't seem to be so easy to re-define the trees appended to these paths from command line to access the systematics.

From CAFExample, there seems to be some support for this, where the tree name can be defined separately:

# paths and names of the input mc files to initialize (eos, using xrootd)
mcFileList: flatNTuple/config/samples/inputFileLists/flatNTuple-Example-mcFileList.txt
mcFileListTreeName: CAFExampleTree
# for using the same input file as above, but on afs (use just one or the other)
#mcPaths: /afs/cern.ch/user/d/dshope/public/forCAFExample/flatNTuple_Example/mc/:CAFExampleTree

However, this seems to be limited to 'mcFileList' which we are not using (and don't particularly like the look of).
I was wondering if one does actually exist for 'mcPaths' option ('mcPathsTreeName'), or if not, then perhaps this can be an idea that could gather some support?