The only related option is that you can tell Opus not to expand the folder when you select it in the tree.
If you expand the folder then I think the tree will always scroll (if required) to show as many child items as possible (without pushing the expanded item off the top, of course). I don't know of a way to stop that, and I suspect it's done by the Windows tree control itself and not something Opus does explicitly. (If you expand something, the assumption is that you want to see and select what's below it, I guess.)