Log Message:
Utilities for implementing Modified Preorder Tree Traversal with your
Django Models and working with trees of Model instances.

MPTT is a technique for storing hierarchical data in a database. The aim is to
make retrieval operations very efficient.

The trade-off for this efficiency is that performing inserts and moving
items around the tree is more involved, as there's some extra work
required to keep the tree structure in a good state at all times.