Arrange the fillers of your choice in the bottom of the Bundt pan (or other pan with a hole in the center) and fill with boiled or distilled water (for clarity.)
If you have leaves that need to be weighted down, use pennies or marbles to hold them down.
Carefully place pan into snow (or simply outside in freezing temps).
Check for progress - speed of freezing obviously depends on temps. If you have weights holding leaves down, be careful not to jostle them around.
Run warm water over outside of Bundt pan to loosen ice. Turn over, tie with ribbon and hang outside! (You'll notice I jostled a penny when it was not done freezing, hence the note in previous photo)
It looks good flipped forward or back.
Edited to Add: I made a second, thinner ice wreath with tree berries and it's much lighter and clearer.