#include <TTree.h>
#include <TLeaf.h>
#include <TBranch.h>
#include <TRandom.h>
#include <TFile.h>


struct Event {
  Int_t nels;
  Double_t val1[100]; //[nels]
  Double_t val2[100]; //[nels]
};

void complextree() {
  TFile *file = new TFile("complextree.root","recreate");
  TTree *mytree = new TTree("mytree","My data tree");
  Event *myevent = new Event;

  mytree->Branch("DATA",0,"nels/I:val1[nels]/D:val2[nels]/D");


  TBranch *branch = mytree->GetBranch("DATA");
  branch->GetLeaf("nels")->SetAddress(&myevent->nels);
  branch->GetLeaf("val1")->SetAddress(myevent->val1);
  branch->GetLeaf("val2")->SetAddress(myevent->val2);

  Int_t nevts=10;
  for (Int_t i=0;i<nevts;++i) {
    myevent->nels = gRandom->Poisson(10);
    for (Int_t j=0;j<myevent->nels&&j<100;++j) {
      myevent->val1[j] = gRandom->Uniform(0,1);
      myevent->val2[j] = gRandom->Gaus();
    }
    mytree->Fill();
  }

  mytree->Write();
  mytree->SetDirectory(gROOT);
  file->Close();
}