These are called "Bottle Trees" and are common in the south. Sometimes, I see one on the way to Franklin.
Bottle Trees are a type of folk art. Translucent bottles are carefully collected and placed on a metal or wood post where there are arms for the bottles to stay. The bottle tree has African origins - the premise being that the bottles glow in the sunlight and evil spirits are drawn to the glass and get trapped inside. There, they can do no harm.
Slaves from the Congo created bottle trees in America by placing bottles on the ends of tree branches. Now, the bottle trees are more formal, using metal or wooden structures.
Skeletons for the trees sell for $90 and upwards.
People in the southern U.S. keep these in their gardens. They don't require water or weeding and add some color to the yard, They can change the bottles and the colors on their whim. The one thing though, is they are warned to take the bottles in during a hurricane or tornado.