#include "TFile.h"
#include "TTree.h"
#include "TClonesArray.h"

class Traj : public TObject {
public:
   int fX;
   int fY;
   int fZ;
   ClassDef(Traj,1);
};

class Detector : public TNamed {
public:
   Detector(const char *name = "not set") : TNamed(name,"title"),fTrajs("Traj") {}

   TClonesArray fTrajs;

   Traj *AddTraj() {
      return new (fTrajs[fTrajs.GetEntries()]) Traj;
   }
      
   void Clear(const char *opt = "") {
      fTrajs.Clear(opt);
   }
   ClassDef(Detector,1);
};

class EventInfo {
public:
   EventInfo() : fEventNumber(0),fRunNumber(0) {}
   void SetRunNumber(Int_t run) { fRunNumber = run; }
   void SetEventNumber(Int_t event) { fEventNumber = event; }

private:
   Int_t fEventNumber;
   Int_t fRunNumber;
};

void Create(const char *filename = "example.root",
            Int_t runnumber = 1, Int_t nevents = 10)
{
   TFile *output = new TFile(filename,"RECREATE");
   TTree *tree = new TTree("tree","tree");
   
   EventInfo *info = new EventInfo;
   info->SetRunNumber(runnumber);

   TObjArray detectors;
   for(Int_t d = 0; d < 10 /* number of detectors */; ++d ) {
      Detector *det = new Detector(TString::Format("det_%d.",d));
      detectors.Add(det);
   }
   tree->Branch("info.",&info);
   tree->Branch(&detectors);

   for(Int_t event = 0; event < nevents; ++event) {
      Int_t detindex = 0;
      TIter next( &detectors );
      Detector *det = 0;
      while( (det = (Detector*)next() ) ) {
         det->Clear();
         for(int t= 0; t < 20 /* number of traj */; ++t ) {
            Traj *traj = det->AddTraj();
            traj->fX = (detindex+1)*(t+1);
            traj->fY = (detindex+1)*(t+4);
            traj->fZ = (detindex+1)*(t+412);

         }
         detindex++;
      }
      tree->Fill();
   }
   output->Write();

   delete output;
}