input: Write a python function to create a trigram model from a list of words.
  assert create_trigram_model(['I', 'wish', 'I', 'may', 'I', 'wish', 'I', 'might']) == {('I', 'wish'): ['I', 'I'], ('wish', 'I'): ['may', 'might'], ('I', 'may'): ['I']}
  assert create_trigram_model(['a', 'b', 'a', 'b', 'a', 'b', 'a']) == {('a', 'b'): ['a', 'a', 'a'], ('b', 'a'): ['b', 'b']}
  assert create_trigram_model(['hello', 'world', 'hello', 'world']) == {('hello', 'world'): ['hello']}
output: def create_trigram_model(words):
      trigrams = {}
      for i in range(len(words) - 2):
          key = (words[i], words[i + 1])
          value = words[i + 2]
          if key not in trigrams:
              trigrams[key] = []
          trigrams[key].append(value)
      return trigrams