from collections import defaultdict

Определить Trie:

_trie = lambda: defaultdict(_trie)

Создать Trie:

trie = _trie()
for s in ["cat", "bat", "rat", "cam"]:
    curr = trie
    for c in s:
        curr = curr[c]
    curr.setdefault("_end")

Поиск:

def word_exist(trie, word):
    curr = trie
    for w in word:
        if w not in curr:
            return False
        curr = curr[w]
    return '_end' in curr

Тест:

print(word_exist(trie, 'cam'))