void TruncateTree(string locInputFileName, string locTreeName, int locNumEntries)
{
	int locNumFinalStateParticles;

	//Get old file, old tree and set top branch address
	TFile *locInputFile = new TFile(locInputFileName.c_str());
	TTree *locInputTree = (TTree*)locInputFile->Get(locTreeName.c_str());
	Long64_t locNumTreeEntries = locInputTree->GetEntries();

	int m_nPart;
	float m_e[3];
	float m_px[3];
	float m_py[3];
	float m_pz[3];
	float m_eBeam;
	float m_pxBeam;
	float m_pyBeam;
	float m_pzBeam;
	float m_weight;

	locInputTree->SetBranchAddress("NumFinalState", &m_nPart);
	locInputTree->SetBranchAddress("E_FinalState", m_e);
	locInputTree->SetBranchAddress("Px_FinalState", m_px);
	locInputTree->SetBranchAddress("Py_FinalState", m_py);
	locInputTree->SetBranchAddress("Pz_FinalState", m_pz);
	locInputTree->SetBranchAddress("E_Beam", &m_eBeam);
	locInputTree->SetBranchAddress("Px_Beam", &m_pxBeam);
	locInputTree->SetBranchAddress("Py_Beam", &m_pyBeam);
	locInputTree->SetBranchAddress("Pz_Beam", &m_pzBeam);
	if(locInputTree->GetBranch("Weight") != NULL)
	  locInputTree->SetBranchAddress("Weight", &m_weight);

	//Create a new file + a clone of old tree in new file
	string locOutputFileName = locInputFileName.substr(0, locInputFileName.size() - 5) + string(".trunc.root");
	TFile *locOutputFile = new TFile(locOutputFileName.c_str(), "RECREATE");
	TTree *locOutputTree = locInputTree->CloneTree(0);

	int locActualNumEntries = locNumEntries;
	if(locActualNumEntries > locNumTreeEntries)
		locActualNumEntries = locNumTreeEntries;

	for(Long64_t loc_i = 0; loc_i < locActualNumEntries; ++loc_i)
	{
		locInputTree->GetEntry(loc_i);
		locOutputTree->Fill();
	}

	locOutputTree->AutoSave();
	delete locInputFile;
	delete locOutputFile;
}