If you are getting picked off by the time they are at the corn pile, then you simply need to make some adjustments like others here have mentioned. Check the wind before you pick a tree. Make sure you your scent isn't blowing into the direction the deer typically approach the bait pile. Get up about 20' in the tree and make sure you have some structure around you breaking up your location in the tree.
If it's a group of deer together then wait until they are all head down in the bait pile before drawing back. If it is just one deer, wait until he or she passes behind a tree and then draw back and pick a tiny spot in his or her vital area and squeeze off a shot.
Make sure you watch exactly where the deer goes after you release. Pick out some reference points i.e trees, brush as to what direction the deer goes. If you have to track it then those reference points will be crucial. If you don't see/hear it crash then wait a good couple hours before you start tracking. There is a good article (stickie) on what to do after the shot.
Good luck.