Hadd RooFit toys ... how?

Dear ROOT experts,
I have the following problem:

I produced n root files containing in one canvas the output histograms of the “plotPull” member function of the RooMCStudy class.
Each root file was produced with k number of toys

I would like to merge all the n root files into 1 root file in order to have the statistics of n*k toys !

“hadd” seems that doesn’t work, in fact I get one root file which contains n-1 subdirectories.

Can you please tell me how can I merge the n identical (in terms of directory layout) files into 1 ?

  • Mauro.