def change_view(self, change_in_depth):
        """Change the view depth by expand or collapsing all same-level nodes"""
        self.current_view_depth += change_in_depth
        if self.current_view_depth < 0:
            self.current_view_depth = 0
        self.collapseAll()
        if self.current_view_depth > 0:
            for item in self.get_items(maxlevel=self.current_view_depth-1):
                item.setExpanded(True)
Change the view depth by expand or collapsing all same-level nodes