how managed nodes in scene manager?

[greetzyl]

hi all:
Tell in my truth,I am a begin learner of IRRLICHT,I already learn all the examples and the namespase "scene" and so on,I kmow we can optimize the scene nodes with octtree etc,but if there is many nodes (e.g camera scene nodes,terrain scene node many Animate model nodes),my problem is:
how the scene manager managed scene so many nodes, and rendered them?
thanks of all!