First thing you need to do is make a hole in the bottom of whatever you have selected to use as your tree topper. Push the stuffing around till you have a deep hole going up into your stuffed animal. Proceed to work the (hopefully clean) toilet paper tube up inside your topper to be. You will have to work it and the stuffing around to get it to work. Once you have it deep enough to properly go onto the top of the tree (3-4 inches should be good) take a small pair of scissors and trim the edges of the tube to make it flush with the opening and there you go one tree topper.
P.S. forgot to mention I did put a little bit of glue around the edge of the tube to secure the material to the tube