{
auto f = new TFile("test.root", "recreate");

auto t1 = new TTree("t1", "t1");
int id1 = 0;
t1->Branch("id", &id1, "id/I");
t1->Fill();
t1->Write();

auto t2 = new TTree("t2", "t2");
int id2 = 0;
t2->Branch("id", &id2, "id/I");
t2->Fill();
t2->AddFriend(t1);
t2->Write();

auto t3 = new TTree("t3", "t3");
int id3 = 0;
t3->Branch("id", &id3, "id/I");
t3->Fill();
t3->AddFriend(t1);
t3->AddFriend(t2);
t3->Write();

f->Close();

}