#include <vector>

void macro() {
    std::vector<TTree*> trees;
    std::vector<TH1F*> hv1;
    std::vector<TH1F*> hv2;
    
    
    float v1;
    float v2;
    TRandom* generator = new TRandom();
    
    for (int i = 0; i < 5; i++) {
        // make a new tree
        TTree* atree = new TTree("t1", "a tree");
        atree->Branch("v1", &v1);
        atree->Branch("v2", &v2);
        
        // fill tree with some values
        for (int j = 0; j < 200; j++) {
            v1 = generator->Gaus(i, 1.0);
            v2 = generator->Gaus(i, 1.0);
            atree->Fill();
        }
        
        // make  new histos
        // make distributions comparing v1, v2 from each tree
        // define binning for each variable
        //use Form to change the names
        TH1F* a_hv1 = new TH1F(Form("hv1_%d",i), "histogram1", 50, 0, 10.0);
        TH1F* a_hv2 = new TH1F(Form("hv2_%d",i), "histogram2", 25, 0, 10.0);
        
        // add tree to list of trees and empty histograms
        trees.push_back(atree);
        hv1.push_back(a_hv1);
        hv2.push_back(a_hv2);
    }
    
    
    
    
    
    for (size_t i = 0; i != trees.size(); i++) {
            trees[i]->Draw(Form("v1>>hv1_%zu",i), "", "goff");
            trees[i]->Draw(Form("v2>>hv2_%zu",i), "", "goff");
        
        
    }
    
    //drawing the hv1's
    hv1[0]->Draw();
    for (size_t i = 1; i != trees.size(); i++)
        hv1[i]->Draw("same");
    
    //drawing the hv2's in another canvaas
    TCanvas *a_canvas = new TCanvas("a_canvas","a_canvas",600,400);
    hv2[0]->Draw();
    for (size_t i = 1; i != trees.size(); i++)
        hv2[i]->Draw("same");
    
}