The Umajin scene tree is used internally to keep track of all the visual objects in the engine. One of the nice features of the language is we can also interrogate and manipulate the scene tree at runtime. This helpful little inspector which Dan created allows us to find and adjust these visual elements.
With the 3.3 engine update Rob has been working on we are also bringing some significant updates to the performance of the scene tree. Both the rendering of objects and resolving touch and mouse events via a high speed spatial traversal.