QStandardItemModel: When there is a lot of rows in a QTreeView, then doing a selectAll(), followed by expanding some items then selectAll() again can cause a performance hit

QStandardItemModel: When there is a lot of rows in a QTreeView, then doing a selectAll(), followed by expanding some items then selectAll() again can cause a performance hit. The first selectAll() is relatively fast, but the second can take considerably longer.