problem finding module tree in the code

[Faezeh1994]

Hi,
when I am running the main.py code, I encounter the following error: Exception has occurred: ModuleNotFoundError
No module named 'tree'
File "\RL-Job-Shop-Scheduling-master\JSS\CustomCallbacks.py", line 3, in
from ray.rllib.env import BaseEnv
File "\RL-Job-Shop-Scheduling-master\JSS\main.py", line 14, in
from CustomCallbacks import *
ModuleNotFoundError: No module named 'tree'.
Not all of them which import from ray.rllib, I have the same issue and it shows that module tree is not found.