Use of real data in TMVA


Apologies for my naive question, since I am quite new to TMVA;

Suppose I am having the MET as variable, and I assign the trees like

factory->AddSignalTree    ( signal,     signalWeight     );
factory->AddBackgroundTree( background, backgroundWeight );

would it be possible to also somehow get an mva output from real data collection, ie a histo that contains MET from real data?

In other words, from mva I get signal+bkg response from MC, but what about data ? How can I do it ?