Building a trie of characters from a list of words

trie.ex

def build_tree(word_list) do
  Enum.reduce(word_list, %{}, fn(word, tree) ->
    word
    |> String.codepoints
    |> place_chars(tree)
  end)
end

def place_chars([], current_node), do: current_node
def place_chars([h | t], current_node) do
  case current_node[h] do
    nil ->
      Map.put(current_node, h, place_chars(t, create_next_node(t)))
    next_node ->
      Map.put(current_node, h, place_chars(t, next_node))
  end
end

def create_next_node([]), do: :leaf
def create_next_node(_), do: %{}