my @list1 = qw/Truck Car Byke/;
my @list2 = qw/Truck Car Scooter/;
my @list3 = qw/Truck Trailer Skates/;

##</code><code>##

Truck
   |_____ Car
   |       |_______Byke
   |       |_______Scooter
   |
   |_____Trailer
           |_______Skates

##</code><code>##

{'Truck' => {
              'Car' => {
                   'Byke' => ?,
                   'Scooter' => ?
              },
             'Trailer' => {
                  'Skates' => ?
            }
}