There is only one master key. It unlocks the doors and trunk, glove box and ignition.
The chances are, somebody before you replaced the ignition cylinder with a used one. You can't go to the dealer and get a key for it, they'll send you another "door" key. A new cylinder with a master key should be about $90 from the dealer. Dealers don't really cut keys based on other keys, they cut a shape based on the VIN. A locksmith can duplicate a key, albeit a worn one.
I had a 240D that had this happen in the past. The lock cylinder was starting to go, so it was a no-brainer to have the cylinder replaced. After that point, just one key.
