[Python] AttributeError: module 'sst' has no attribute 'train_reader'

I am very new to sentiment analysis. Trying to use Stanford Sentiment Treebank(sst) and ran into an error.

from nltk.tree import Tree
import os
import sst
trees = "C:\\Users\m\data\trees"
tree, score = next(sst.train_reader(trees))


[Output]:

AttributeError Traceback (most recent call last)
<ipython-input-19-4101f90b0b16> in <module>()
----> 1 tree, score = next(sst.train_reader(trees))

AttributeError: module 'sst' has no attribute 'train_reader'

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