code: def _add_to_tree(tree, word, meaning):
      '''
      We build word search trees, where we walk down
      the letters of a word. For example:
        你 Good
        你好 Hello
      Would build the tree
           你
          /  \
        You   好
               \
             Hello
      '''
      if len(word) == 0:
          tree[''] = meaning
      else:
          _add_to_tree(tree[word[0]], word[1:], meaningf _add_to_tree(tree, word, meaning):
      '''
      We build word search trees, where we walk down
      the letters of a word. For example:
        你 Good
        你好 Hello
      Would build the tree
           你
          /  \
        You   好
               \
             Hello
      '''
      if len(word) == 0:
          tree[''] = meaning
      else:
          _add_to_tree(tree[word[0]], word[1:], meaning)
docs: We build word search trees, where we walk down
      the letters of a word. For example:
        你 Good
        你好 Hello
      Would build the tree
           你
          /  \
        You   好
               \
             Hello