code: def change_view(self, change_in_depth):
          
          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)
docs: Change the view depth by expand or collapsing all same-level nodes