Version 2.0 features a treemap for files bigger than 100k. Thanks neurofuzzy for the php-treemap source code.

For those who want to skip the original technical paper on Tree visualization with Tree-maps:

The traditional approach to representing tree structures is as a rooted, directed graph with the root node at the top of the page and children nodes below the parent node with lines connecting them has a long discussion about this standard representation, especially why the root is at the top and he offers several alternatives including brief mention of a space-fillling approach . However, the remainder of his presentation and most other discussions of trees focus on various node and edge representiation. By contrast, this paper deals with a two-dimensional (2-) space-filling approach in which each node is a rectangle whose area is proportional to some attribute such as node size.

Shneiderman, B. (March 1991)
Tree visualization with treemaps: a 2-d space-filling approach
ACM Transactions on Graphics, vol. 11, 1 (Jan. 1992) 92-99.