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.

Followup: remove redundant folders from access list.