#include<map>

void WriteTreeWithMap(){

    TFile* newfile = new TFile("testfilewithmap.root","RECREATE");
    TTree* newtree = new TTree("newtree","a tree with a map");

    std::map<int,int> somemap;
    somemap.clear();

    int bsize=256000;
    int split=0;
    
    newtree->Branch("somemap", "std::map<int,int>", &somemap, bsize, split);

    for (int i=0; i<30; i++){
        somemap[i] = i*i;

        if(i%5==4) {
            std::cout<<"i somemap[i] somemap.size() "<<i<<" "<<somemap[i]<<" "<<somemap.size()<<std::endl;
            newtree->Fill();
            somemap.clear();
        }
    }

    newfile->Write();
    newfile->Close();

}