RooSimultaneous fit on categories with different x variables - bad combined data

Thank you for the feedback. We will add an example for this.
One another thing is that is not efficient to build RooDataHist objects with multi-variables. For example for 2 variables with n1 and n2 bins, RooFit will allocate n1 x n2 bins. It is more convenient to use a weighted RooDataSet with a weight equal to the number of bins.

Best regards