In this report, we discuss Tree Music, an interactive computer music installation created using GAIA (Graphical Audio Interface Application), a new open-source interface for controlling the RTcmix synthesis and effects processing engine. Tree Music, commissioned by the University of Virginia Art Museum, used a wireless camera with a wide-angle lens to capture motion and occlusion data from exhibit visitors. We show how GAIA was used to structure and navigate the compositional space, and how this program supports both graphical and text-based programming in the same application. GAIA provides a GUI which combines two open-source applications: RTcmix and Perl. Keywords Composition, new interfaces, interactive systems, open source, Real time audio, GUI controllers, video tracking