Bundles items are not split when the DOMS would normally performing an order split.
Items can be bundled via the custom-service concept by adding items to a custom service and defining it as "bundled" within the order. The line items that should be bundled have to be a part of the orderLineItems within the order.
Example on how a bundling customService list might look like within an order
Example how an order might look like when it contains item bundles
Let's imagine you want to send two buquets of flowers to your friend Peter Parker. One with tulips and one with red roses, bundled with a bottle of champagne. Then your order might look like this: