Trees are something most people can identify with.
Get a dried limb with several branches - the size will be according to availability and the space you have to store it. Put it in a bucket or can filled with sand or stones so that the whole stands upright. Decorate with leaves, wheels, stupas, mandalas, streamers, stars, moons, suns, bless it with glitter, etc. Put a Buddha image sitting underneath the tree. Bless it with more glitter, water, confetti, chanting, incense, bowing, etc.