void
create()
{
    TFile* file = TFile::Open("test_highmem_cluster.root", "RECREATE");

    TTree* tree = new TTree("t", "t");

    tree->SetAutoSave(20000);

    std::vector<std::string> s;
    tree->Branch("s", &s);

    for (Long64_t i = 0; i < 1000000; ++i)
        tree->Fill();

    file->Write();
    file->Close();
}