Source Tree Visualizer is an open source project that visualizes source control repositories as real growing trees. It started as a research project at my former startup Discursive Labs, but we felt it was too cool to let sit around somewhere on a hard drive.
You can compile this in any unix-like environment which supports a few standard libraries. See the top level directory for example config files for generating images.
See examplescripts for example usages for simpletree