Draw plots with multi input root files

I want to draw a plot with multi-input files after I failed to use “hadd” to merge these input files…

The following is the basic example of one plot drawing with one root file. What should I do if I want to draw this plot with multi-input files?

TCanvas *c = new TCanvas("c", "fill in the plots", 0, 0, 400, 600);
c->GetFrame()->SetBorderSize(22);
TPostScript *ps = new TPostScript("CV.ps", 111);
TFile* sig = new TFile("file1.root", "READ");
TTree *tree = (TTree *) gDirectory->Get("T");

tree->Draw("CV >> h1temp(100,0,5)","EtSum<5000 ");
TH1F* h1 = (TH1F *) gDirectory->Get("h1temp");
    h1->SetTitle("CV Veto system");
    h1->GetYaxis()->SetTitle("Entries");
    h1->GetYaxis()->SetTitleOffset(3);

http://root.cern.ch/root/html/TChain.html#TChain:TChain@2
http://root.cern.ch/download/doc/ROOTUsersGuideHTML/ch12s24.html
http://root.cern.ch/drupal/content/how-use-chains-list-files

Got it.

Thanks a lot.