It is one way to do it. With the approach you suggested, it means going through this process:

1. fetch an entry
2. find any children
3. for each child, call step 1

And with an additional table, the steps are?

1. fetch an entry
2. fetch all descendants of that entry (gives a collection)
3. build a tree doing ... what exactly? Probably a select to get its immediate parent.

There. :-)

update - having read the Nested Set Model of Trees - well, that's one way to do it. You have to jump through hoops still to get your data into a tree structure suitable to be displayed in a TT template. But anyways, trading simplicity and additional database calls for just one call (which I doubt would satisfy the OP's requirements) and more code complexity is something I would do only if I had proven the fact that multiple queries are the bottleneck in that application.

update 2: Thinking about it, building a tree given the parent_id in each record would probably be pretty simple, so there's no point discussing your improvement.

cheers,

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