Which of the following ranks is not represented by the insignia containing an oak leaf?

The rank that is not represented by the insignia containing an oak leaf is Brigadier General (BGEN). In the U.S. military, the insignia for a Brigadier General features one silver star, which signifies the rank. In contrast, the oak leaf insignia is used to represent the ranks of Major and Lieutenant Colonel, with the silver-colored oak leaf indicating Lieutenant Colonel and the gold-colored oak leaf indicating Major. Colonel, on the other hand, is represented by a distinctive eagle insignia. The oak leaf is specifically associated with the ranks of Major and Lieutenant Colonel, clearly distinguishing them from the Brigadier General rank and its unique star insignia.