unnecessary update in QAbstractItemView::doItemsLayout() causes performance issue

#include <QApplication>
#include <QTreeWidget>
#include <QTime>
#define NUM 3000

class Work : public QObject
{
public:
        Work() :num(0)
        {
                tree = new QTreeWidget;
                tree->show();
                time.start();
                for( int i = 0; i < NUM; i++)
                {
                        new QTreeWidgetItem(tree, QStringList(QString("item: %1").arg(i)));
                        qApp->processEvents();
                }
                qDebug("Finish. Time elapsed: %d ms", time.elapsed());
        }

private:
        QTreeWidget *tree;
        int num;
        QTime time;
};
int main(int argc, char* argv[])
{
        QApplication a(argc, argv);
        Work work;
        return a.exec();
}