my %dict; # A reverse index on %dict by id.
while (my $line = <$fh>) {
    my ( $id, $parent, $term ) = split ' ', $line, 3; # Fixed from -3 per sauoq

    $dict{$id}{'id'}     = $id;
    $dict{$id}{'parent'} = $parent;
    push @{$dict{$parent}{'children'}}, $dict{$id};
}

use Data::Dumper;
print Dumper( \ %dict );