To put ribbon on a Christmas tree horizontally, you will need to start by taking a long piece of ribbon and wrapping it around the tree trunk. Make sure to start at the top of the tree and work your way down, wrapping the ribbon around the trunk in a horizontal direction. Once you reach the bottom of the tree, tie off the ribbon and cut off any excess. Next, take another piece of ribbon and wrap it around the tree trunk in a horizontal direction, but this time start at the bottom and work your way up. Tie off the ribbon and cut off any excess.