We have a mature weeping birch in our front yard. It drops lots of long, thin, flexible twigs, especially after a storm.
I was sitting in the front while the kids played in the little plastic sandbox and decided to make a wreath.
I gathered a bunch of the longer more flexible strands into a pile. I wrapped a couple to form a circle and secured it with a bit of thin wire. I used small pieces of wire to add more twigs to the circle, making it rounder and fuller.
After awhile, I started wrapping small bundles of long, flexible twigs around the wreath, tucked in the loose ends, and secured anything that wouldn't stay with a little more wire.
Once it was thick enough, my attention span was shot, or the kids needed me (I forget which happened first), I hung the wreath on the door with a little more wire.