You have to manually write some code to recursively close all nodes. I've been not using Tk for some time, so I can only give you some pseudo-code:

sub close_all {
  my $node = shift;
  foreach my $child ($node->method_to_get_its_children) {
    close_all($child);
  }
  $node->method_to_close_itself;
}
[download]