The presence of multiple stellar populations is now well established in most 
globular clusters in the Milky Way. Here we show that the Oosterhoff period 
groups and the double red clump observed in the halo and bulge, respectively, 
are another manifestations of the same multiple population phenomenon 
observed in halo globular clusters. We will discuss the implications of 
this result on the formation of the halo and bulge of the Milky Way, 
and on the stellar populations of early-type galaxies.