String similarity calculation
One thing I'd suggest is to allow a word to be inserted inside __init__, rather than force the user to always call .insert(word). You can still allow for creating an empty TrieTree. Just make word an optional parameter, and ignore it if it's empty:

def __init__(self, word=''):
    self.root = TrieNode()
    if word:
        self.insert(word)


now you could create your tree in one line:

index = TrieTree(word)