Tree Query question

I'm trying to work through a tree query in PL*SQL and getting nowhere. If you are familiar with the Work Breakdown Structure (WBS) concept, then you quickly understand what I'm doing.

Can anybody give me a hand with this? E-mail replies are encouraged, even if you also reply to the newsgroup.

Thanks.

Sincerely,
Randall

Data look something like this.

Job Parent Spent

10    NULL      100  -- top level has NULL parent  WBS 10
20    10        500  -- child                          10.20
27    20        700  -- grandchild                     10.20.27
32    27         50  -- great grandchild               10.20.27.32
21    20        200  -- a 2nd branch from job 20       10.20.21

There is no limit to the breadth or depth of the tree, although as a practical matter I suspect about 10 or 15 levels will be the depth limit reached and 20 or 30 will be the practical limit for breadth.

I want to construct a report similar to this, but can't see the coding logic to doing it. Can you point me in the right direction?

Job      Spent_by_Job_&_Progeny
10       1550         -- spent by job 10 and all of its descendents
20       1450         --    "         20         "
21        200         --    "         21.  It has no descendents.
27        750         --    "         27 and all of its descendents.    
32         50         --    "         32.  It has no descendents.