Two scenarios have been suggested to explain the double red clump (RC) phenomenon observed in the Milky Way bulge. One is the X-shaped bulge model, and the other is multiple population model as is observed in globular clusters (GCs). Because these two scenarios imply very different pictures on the formation of the bulge, understanding the origin of the double RC is of crucial importance. In order to investigate the origin of the double RC, we performed low-resolution spectroscopy for stars in the two RC regimes, and measured CN, CH, and Ca band strengths. We found that the stars in the two RCs show (1) a significant (> 5.3 sigma) difference in CN strength, but (2) negligible differences in CH and Ca abundances. This chemical pattern is in contrast to that expected in the X-shaped bulge scenario, but is fully consistent with the behavior predicted in the multiple population model.