class test : public TObject { 
public: 
test() {fGraph=0;}  <=============
~test() {}; 
SetGraph(TMultiGraph *p) {fGraph = p;} 
SetX(Double_t x) {fX = x;} 
TMultiGraph* GetGraph() {return fGraph;} 
private: 
Double_t fX; // 
TMultiGraph* fGraph; //|| 
}; 

void testTMultiGraph (Int_t MaxEv=10) { 
test *event = new test(); 
TTree* fRecoTree = 0; 
TFile *fFile = new TFile("testTMultiGraph.root","RECREATE"); 
fRecoTree = new TTree("tree","TestTree"); 
fRecoTree->Branch("events","test",&event); 
Double_t x[10],y[10]; 
Int_t ev(0); 
while (ev++<MaxEv) { 
for (Int_t i=0;i<10;i++) { 
x[i] = i; 
y[i] = i*i; 
} 
TGraph *g1 = new TGraph(10,x,y); 
g1->SetMarkerSize(.5); 
g1->SetMarkerColor(kRed); 
g1->SetMarkerStyle(23); 
TMultiGraph *gAll = new TMultiGraph("TestGraph",""); 
gAll->Add(g1,"lp"); 
event->SetGraph(gAll); 
event->SetX(ev); 
fRecoTree->Fill(); 
cout << "Event # " << ev << endl; 
} 
fFile->Write(); 
delete fFile; 
} 

void Plot(Int_t ev=0) { 
TFile f("testTMultiGraph.root"); 
TTree *p = (TTree*)f.Get("tree"); 
test* event = 0; //<============
p->SetBranchAddress("events",&event); 
//p->LoadTree(ev); // crashes here... 
p->GetEntry(ev); // <=============== 
TMultiGraph* fGraph = event->GetGraph(); 
fGraph->Draw("alp"); //<==========
}