#define memorydepth 10
class MY_DATA{
  public:
    Double_t peak;
    Double_t wvf[memorydepth];
    Int_t selection;

    MY_DATA();
    string tobranch = "peak/D:wvf[" + to_string(memorydepth) + "]/D:selection/I";

    void setBranchName(Int_t n = memorydepth){
      tobranch = "peak/D:wvf[" + to_string(n) + "]/D:selection/I";
    }

};


MY_DATA::MY_DATA(){

  for(Int_t i = 0; i<memorydepth; i++){
    wvf[i]=0;
  }
  peak = 0;
  selection = 0;
}


void example_tree_read(){
  MY_DATA data;
  TFile *fread = new TFile("example_tree.root","READ");
  TTree *t1 = (TTree*)fread->Get("t1");
  TBranch *b = t1->GetBranch("data");
  b->SetAddress(&data);
  for(Int_t i = 0; i < t1->GetEntries(); i++){
    b->GetEvent(i);
      cout << data.peak << " "; // no problem here
      cout << data.selection << "\n"; // no problem here
  }
  fread->Close();
}