Modified Pre-order Tree Transversal

[eluser]adamp1[/eluser]
I just want to ask has anyone used this method for a database tree? Also how do you get around the problem of having to have a root node? What I mean by this is you can only store a single tree in a database table. This means the root node is pointless.

Here's an example, if I want to store category information for a product database. Using MPTT I would have to have a tree like so:

Code:

Categories
  Fruit
  Chocolate
    Black
    White
  Sweets
    Red
    Yellow

As you can see the root node is totally pointless? So does anyone use this method for storing trees?