#include <string>
#include "TTree.h"

void tree_str_test_2 () {
  TTree *t  = new TTree("t","tree t");

  std::string str_1, str_2;

  t->Branch("str_1",&str_1);
  t->Branch("str_2",&str_2);
  
  str_1 = "aa1";
  str_2 = "aa2";
  t->Fill();

  str_1 = "bb1";
  str_2 = "bb2";
  t->Fill();

  str_1 = "aa1";
  str_2 = "bb2";
  t->Fill();

  t->Scan();
  t->Draw("str_1:str_2","","colz");
}