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

Truck
   |_____ Car
...
   |
   |_____Trailer
           |_______Skates

{'Truck' => {
              'Car' => {
...
                  'Skates' => ?
            }
}