Interesting - its a secondary main branch, isn't it. It won't kill the tree if you remove it, but a word of warning - check the whole tree from top to bottom first, looking for any signs of damage, rot, infection, seeping, oozing or anything else unusual. Sometimes plants throw out a second mainstem like this because there's damage/infection on the other one.

Is this near the house? They reach an eventual height of 80 feet with all the foliage at the top, so it shouldn't be near a building.