ex()
{
  gSystem->Load("libGeom");
  TGeoManager *geom = new TGeoManager("geom", "test");

  TGeoMaterial *vacuum = new TGeoMaterial("Vacuum", 0, 0, 0);
  TGeoMedium *mVac = new TGeoMedium("GVAC", 0, vacuum);

  TGeoVolume *top = gGeoManager->MakeBox("Top", mVac, 1000., 1000., 1000.);
  gGeoManager->SetTopVolume(top);
  gGeoManager->SetTopVisible(0);

  box1 = gGeoManager->MakeBox("box1", mVac, 100, 100, 100);
  box1->SetLineColor(kGray);
  box1->SetTransparency(70);
  box2 = gGeoManager->MakeBox("box2", mVac, 50, 50, 50);
  box2->SetLineColor(kRed);

  box1->AddNode(box2, 1);
  top->AddNode(box1, 1);
  
  top->CheckGeometry(1E+3);

  top->Draw("ogl");
}