Robert,

B-Trees and B+Trees are self balancing. Inserting a lot of records inorder though would cause lots of rebalancing to occur.

The imbalanced trees you are thinking of can happen with simple binary trees where you don't have any code to keep the tree balanced.

>I seem to remember that, for certain index types (paged B+ I think), an ordered insert is the worst-case scenario (i.e. results in the worst performance) resulting in a wildly imbalanced 'tree' so that instead of (say) four disc accesses to reach any record, you must make a much larger number.