Branch indicator not centered in QTreeView with custom icon size

#include <QtWidgets> 
#include <QtGui> 
#include <QPixmap>

int main(int argc, char *argv[]) 
{ 
   QApplication a(argc, argv); 

   const QSize iconSize(32, 32);
   QPixmap icon(iconSize);
   icon.fill(Qt::red);

   // Build a model 
   QStandardItemModel model(5, 1); 
   for (int r=0; r<5; r++) { 
       QStandardItem* item = new QStandardItem("Parent"); 
       item->setIcon(icon);
       for (int i=0; i<3; i++) { 
           QStandardItem* child = new QStandardItem("Child"); 
           item->appendRow(child); 
       } 
       model.setItem(r, 0, item); 
   } 

   QMainWindow window; 
   QTreeView* tree = new QTreeView();
   tree->setIconSize(iconSize);
   tree->setModel(&model); 
   window.setCentralWidget(tree); 
   window.show(); 
   return a.exec(); 
}