let ex = Node (false,
           Node (false,
             Node (true, Nil, Nil, Nil, Nil),
             Node (true, Nil, Nil, Nil, Nil), 
             Nil,
             Node (false,
               Node (true, Nil, Nil, Nil, Nil),
               Nil,
               Node (true, Nil, Nil, Nil, Nil),
               Nil)),
           Node (true, Nil, Nil, Nil, Nil), 
           Node (true, 
             Node (true, Nil, Nil, Nil, Nil),
             Node (false, 
               Nil, 
               Node (true, Nil, Nil, Nil, Nil),
               Nil, 
               Node (true, Nil, Nil, Nil, Nil)),
             Nil, 
             Node (true, Nil, Nil, Nil, Nil)), 
           Nil);;

let lst = [[A; A]; [A; C]; [A; T; A]; [A; T; G]; [C]; [G]; [G; A]; [G; C; C]; [G; C; T]; [G; T]];;