#
# A
# |___ B 
# |    |___ C <-- access
# |    |___ D
# |___ E <-- access
#      |___ F  ---- G
#

folders = [
  ('A', None),
  ('B', 'A'),
  ('C', 'B'),
  ('D', 'B'),
  ('E', 'A'),
  ('F', 'E'),
  ('G', 'F'),
]

access = {'C', 'E')

Given a folder name, return TRUE|FALSE is user have access

Follow up:  access = {'C', 'E', 'F') but 'F' is redunant. How to shorten the access list.