code: def display_hierarchy_helper(root, parent_id_to_children, depth):
    
    print '%s%s (%s)' % ('%s+--' % ('|'.join(['  '] * depth)),
                         root['name'], root['id'])
  
    # Recurse for each child of this root that has children.
    for child in parent_id_to_children.get(root['id'], []):
      display_hierarchy_helper(child, parent_id_to_children, depth + 1)
docs: Recursive helper for displaying the hierarchy.
  
    Args:
      root: The current root ad unit.
      parent_id_to_children: The overall map of parent ids to children.
      depth: The current depth.