type arbre =  Noeud of bool ref  * (char * arbre) list ref

(*Not necessary but left here in case *)
let rec creer_branche cs = match cs with
  | [] -> vide ()
  | [c] -> Noeud (ref false, ref [c, Noeud(ref true, ref [])])
  | c :: cs' -> Noeud (ref false, ref [c, creer_branche cs'])

let ajouter arbre mot =
    let get_tuple_list (Noeud(a, b)) = b in
    let add arbre mot = match arbre, mot with
    | Noeud(a, b), mot' -> (!(get_tuple_list (creer_branche (explode mot))) @ !b; ())
  in add arbre mot