use strict;
use warnings;
use Data::Dumper qw/Dumper/;

my $input = get_input();

my $second = $input->{1929};

my ( $tree, @roots );

while ( my ( $id, $attr ) = each %$second ) {

    my $boss_id   = $attr->{boss};
    my $name      = $attr->{name};    

    unless ( $boss_id ) {
        push @roots, $name;
        next
    }

    my $boss_name = $second->{$boss_id}->{name};

    $tree->{$boss_name}{$name} = $tree->{$name} //= {};
}

#$Data::Dumper::Indent   = 1;
$Data::Dumper::Terse     = 1;
#$Data::Dumper::Pad      = '#';
$Data::Dumper::Quotekeys = 0;
#$Data::Dumper::Pair      = ' : ';

print Dumper { map { $_ => $tree->{$_} } @roots };

sub get_input{
    return
{
  1929 => {
            1 => { boss => 1929, name => "Hermes" },
            2 => { boss => 1, name => "Leela" },
            3 => { boss => 1929, name => "Amy" },
            4 => { boss => 1, name => "Zoidberg" },
            480 => { boss => 2, name => "Fry" },
            1919 => { boss => 2, name => "Bender" },
            1929 => { boss => 0, name => "Professor" },
            3968 => { boss => 1929, name => "Cubert" },
            4425 => { boss => 1, name => "Dwight" },
          },
};
}