//Read the information off the existing TFile

void TFileRead()
{
	TFile *filename = new TFile("filename.root", "READ"); //READ
	TTree *treename = (TTree*)filename->Get("treename");

//	TH1F* histname = (TH1F*)treename->GetHistogram("histname");

	treename->Draw("histname");
	treename->GetHistogram();	
}