I have a Diesel E90 which does have a dipstick, but the petrol E90's do not.

In a petrol E90 you can check the oil level via the onboard computer.

The thing that really surprised me with the dipstick is that in the manual it says that you should check the oil level when the engine is warm. In all my previous cars you always checked the oil level when the engine was cold and all the oil had dripped back into the sump!