Can you provide an example of how a simple multilevel index might be structured without using B-trees, and why B-trees are generally preferred?

A simple, non-B-tree multilevel index might involve creating an index on a primary key, and then another index on a secondary key that points to the primary key index. For example, an index on `customer_id` (primary) and another index on `email_address` that, when a match is found, returns the `customer_id`, which is then used to look up the record in the primary index. B-trees are generally preferred because they are self-balancing, ensuring predictable performance even with frequent data modifications. They also handle large datasets more efficiently due to their optimized node structure and branching factor, and are naturally suited for disk-based storage.