Remove the lid from the mason jar and cut a piece from the styrofoam ball to fit inside. Cover with decoupage and fake snow. Hot glue to the inside of the mason jar lid. Cut the top off of the Christmas tree and hot glue to the top. Allow this to dry completely.
Add some of the small foam balls to the inside of your jar and replace the lid. Then use hot glue to add a ribbon accent around the lid before your hang on your tree.