Slight change leads to segmentation fault in qt example

Hello.
I have just compiled the simpetreemodel example that comes with the qt sources. That worked fine.
But this slight change to the treemodel constructor (the last two lines with the x variable) gives me a segmentation fault. Does anyone know why? To me it is a mystery and I must have failed to understand something very basic?

Code:

---

TreeModel::TreeModel(const QString &data, QObject *parent)
    : QAbstractItemModel(parent)
{
    QList<QVariant> rootData;
    rootData << "Title" << "Summary";
    rootItem = new TreeItem(rootData);
    setupModelData(data.split(QString("\n")), rootItem);
 
    TreeItem* x = new TreeItem(rootData);
    rootItem->appendChild(x);
}

---

I should add that I just wanted to try to add an extra item. But it seems that did not work.