'Change the view depth by expand or collapsing all same-level nodes'

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)
