traverse($in, 0, 0, sub {print ' ' x $_->{dept},'-',$_->{comm},"\n";});

... later in the code...

traverse($in, 0, 0, sub {$sth->execute($dept, $comm)});

##</code><code>##

sub _print {
   print ' ' x $_->{dept},'-',$_->{comm},"\n";
}

traverse($in, 0, 0, \&_print);

##</code><code>##

sub print_tree {
   push(@_, 0, 0, sub {print ' ' x $_->{dept},'-',$_->{comm},"\n";});
   &traverse;
}

print_tree($in);