for ( keys %category_hash ) {
   my $first_lvl = $category_hash{$_};
   print "$_\n";

   for ( keys %{ $first_lvl } ) {
      my $second_lvl = $first_lvl->{$_};
      print ' ' x 3 . "$_"\n";

      for ( keys %{ $second_lvl } ) {
         print ' ' x 6 . "$_ : $second_lvl->{$_}\n";
      }
   } # END for keys $first_lvl
}    # END for keys %category_hash