CLONE - setSelected() in QTreeWidget is very slow

If there is lot of data in QTreeWidget, setSelected() to many items is extremely slow. For example selecting 6000 items takes about 21 seconds with following code:

    QTreeWidgetItemIterator it(tree);
    while (*it) {
        (*it)->setSelected(true);
        ++it;
    }

Please find attached an example which reproduces this issue.