let mult lsts  = 

    List.rev lsts 

    |> List.fold  (fun acc h -> 

           h 

           |> List.collect (fun e -> acc |> List.map (fun l -> e :: l ) ) 

         ) [[]]

let nestedApply f lsts = mult lsts |> List.collect f

​

[[1 .. 5];[6;7];[11;12]]

|> nestedApply id

|> printfn "%A"