Mobile communication systems are often susceptible to high level of noise injected by adversaries, known as jamming attack. Jamming is difficult to prevent in broadcast networks because a user that can decode a transmission can also jam the transmission. In this paper, we describe a code tree system that helps the physical layer circumvent jammers. This system works with any spread-spectrum communications system. In our system, the transmitter has more information than any single receiver. Each receiver cooperates with the transmitter to detect any jamming that affects that receiver. Our scheme mitigates the jamming attack while allowing the transmitter to transmit on fewer codes than the number of users. We simulated our system in a theoretical setting using MATLAB. The result shows significant improvement over naively transmitting on a single shared code.