I'm not clear on how the Render Tree in XSI got to be called that, but I think there was a renderman-related product Shader Tree or ShadeTree that was hot at that time. We have often discussed internally that Render Tree was not a good name, you'd expect that to control the whole render process, not just edit one shader,
Hypergraph/HyperShade might have called that for the same reason that links in the web browser are called Hyperlinks: was trendy in the 1990s. But an hypergraph is also an actual math term, a graph where any edge can connect anywhere.
