Searching a trie of characters for a string

trie.ex

def valid_word?("", _), do: true
def valid_word?(word, tree) do
  chars = String.codepoints(word)
  case check_char(chars, tree) do
    false ->
      false
    _ ->
      [_ | t] = chars
      valid_word?(Enum.join(t), tree)
  end
end

def check_char(_, :leaf), do: false
def check_char([], _), do: true
def check_char([h | t], current_node) do
  case current_node[h] do
    nil ->
      true
    next_node ->
      check_char(t, next_node)
  end
end