Selecting tree data - Mailing list pgsql-general

I'd like to store some tree data in my database.  I want to be able to
sort the data but maintain a tree structure.  So for example, if I
order by a timestamp, I should get

- parent1
   * child1
   * child2
   * child3
- parent2
  * child4
  * child5

and if I reverse the sort order, I get

- parent2
  * child5
  * child4
- parent1
  * child3
  * child2
  * child1

Is it possible to pull all the data like that with one query?  How do
I need to structure the table, and what query do I have to run in
order to make it happen?

Pat