Add popcorn and oil to a pot and cover.
Turn the burner to medium high heat.
Once popcorn starts to pop, shake the pot back and forth on the burner while keeping the lid closed. This will keep the popcorn sliding around and prevent burning.
Once the popping dies down, remove from heat and let cool.
Once popcorn is cool, thread a needle while leaving the thread attached to the spool. This is to allow for the proper length of garland. It's almost impossible to tell how long to cut the string to ensure all of the popcorn fits.
Poke the needle through the center part of each individual piece of popcorn pulling them down as you go.
Once you've threaded all of the popcorn, tie off the string around the last and first pieces of popcorn and knot so that the popcorn doesn't come off.
Hang on the tree however you like.