Just take the top off of the ornament and put the rubies into the ornament and you’re done! I may glue my top on if I have any trouble, but so far so good!
I am more of a Hufflepuff myself, but the Gryffindor colors are so Christmasy and fun so this year I did more of a Gryffindor themed tree. One day I’ll have to do a Hufflepuff one. . .
To see more of my Harry Potter Christmas tree posts check out my December 2018 posts.