Glue scraps of cardboard together to form a square.
Draw a spiral on the cardboard and cut it out.
Poke holes in the sides of the spiral and pull strings through.
Pull up the spiral with the help of the strings.
Attach wooden beads (or similar) to the strings to support the spiral so it doesn't sag.
Hang the tree on a hook (e.g. on a shelf).
Decorate the tree with strips of green paper and drawings.
Provide the edge with cardboard hooks so that the tree can be hung with Christmas decorations.