Have multi-column QTreeWidget root items

I am using a QTreeWidget to display items in categories. Items will use several columns, but I want categories (ie. root items) to use the full width of the widget. How can I do that? And a piece of my code: ``` class BugsList(QtGui.QDialog): def __init__(self, parent, reports): super(BugsList, self).__init__(parent) # Call QDialog constructor self._tree = QtGui.QTreeWidget(self) self._tree.setColumnCount(NUMBER_OF_COLUMNS) # ... for category, bugs in reports: category_widget = QtGui.QTreeWidgetItem(self._tree, [category]) # ... ``` Here is a screenshot of the current state of my application: