my $lol =$vocabulary->tree_to_lol;
my $code =$vocabulary->tree_to_lol_notation({multiline=>1});
print "$code\n";
__END__
[
  [
    [
      [
        'dog'
      ],
      'domestic'
    ],
    [
      [
        'tiger'
      ],
      'wild'
    ],
    'animals'
  ],
  [
    'sciences'
  ],
  [
    'vehicles'
  ],
  'vocabulary'
],