sub print_tree{
   my ($sub, $tab) = @_;
       foreach (@{$found{$sub}}){
                print "$tab$_\n";
                $tab .= "\t";
                print_tree($_, $tab);
                }
       return;
       }

##</code><code>##

a
  c
    f
    e
b
etc...

##</code><code>##

a
  c
    f
  e
b
etc...