I'm not entirely sure what your saying?
tree? what kind of tree. Object heirachy? The reason I think your talking about this is because of this line.
"some games only need the single line of gravity in them with many hundreds of objects, "
If this is the case. Then I also made the request for a Scengraph technology under the topic of [suggestion Pin] Theory or Relativity. If I'm wrong. Then I have no idea what your talking about :(