Status tips are not shown for QHeaderView

#include <QtGui>

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

    QMainWindow w;

    QTreeView tree;

    QStandardItemModel model(4, 2);
    for(int x = 0; x < model.rowCount(); ++x) {
        for(int y = 0; y < model.columnCount(); ++y) {
            QStandardItem *item = new QStandardItem(QString("item %0 %1").arg(x).arg(y));
            item->setData(QString("status tip for item %0 %1").arg(x).arg(y), Qt::StatusTipRole);
            model.setItem(x, y, item);
        }
    }

    for(int i = 0; i < model.columnCount(); ++i) {
        model.setHeaderData(i, Qt::Horizontal, QString("column %0").arg(i));
        model.setHeaderData(i, Qt::Horizontal, QString("status tip for column %0").arg(i), Qt::StatusTipRole);
    }

    tree.setModel(&model);
    tree.viewport()->setMouseTracking(true);

    w.statusBar();
    w.setCentralWidget(&tree);
    w.show();

    return app.exec();
}