The library can be found in /js/lib/DataStructures.Tree.js
A primary purpose of this library is the ability to be able to convert from a flat self-referencing table to a hierarchical tree, which in turn can be decorated.
The illustrating example in /index.html shows a flat table representing the code in the DataStructures library being converted to hierarchical json and decorated in a way that is suitable for d3 circle packing.
Tests for DataStructures.* are written in QUnit and can be found in /js/lib/tests/test.html.
more info on my blog