It just so happens that there is a networkx utility that can publish a tree structure represented as a networkx directed graph in the JSONic form that d3.js works with (networkx.readwrite.json_graph), so I had a little play with the code I used to generate Freemind mind maps from OpenLearn units and refactored it to generate a networkx graph, and from that a d3.js view:

(The above view is a direct copy of Mike Bostock’s example code, feeding from an automagically generated JSON representation of an OpenLearn unit.)

For demo purposes, I did a couple of views: a pure HTML/JSON view, and a Python one, that throws the JSON into an HTML template.

The d3.js JSON generating code can be found on Scraperwiki too: OpenLearn Tree JSON. When you run the view, it parses the OpenLearn XML and generates a JSON representation of the unit (pass the unit code via a ?ucode=UNITCODE URL parameter, for example https://scraperwiki.com/views/openlearn_tree_json/?unit=OER_1.

The Python powered d3.js view also responds to the unit URL parameter, for example:
https://views.scraperwiki.com/run/d3_demo/?unit=OER_1

The d3.js view is definitely very pretty, although at times the layout is a little cluttered. I guess the next step is a functional one, though, which is to find how to linkify some of the elements so the tree view can act as a navigational surface.