Errr...you didn't tell us which plant this is, so I'll make a stab in the dark and guess that it's Crocosmia. They do this - you can take the top one and replant it, and get rid of the bottom one, or try planting it elsewhere. I dug up a huge clump last spring, and counted 7 corms on top of each other. They do need to be split occasionally, or you'll get non-flowering corms.