1. Decorative or artistic use: Some people may hang some decorations or artworks, including knives, on trees. This may be out of personal preference, or it may be to create a special atmosphere or style.
2. Feng Shui or superstitious beliefs: In some Feng Shui or superstitious beliefs, knives are considered to have the function of exorcising evil spirits, driving away disasters or protecting. Therefore, some people may hang knives on trees, hoping to pray for peace and good luck.
3. Warning or deterrent effect: In some cases, someone may hang a knife on a tree as a warning or deterrent symbol. This may be to show your vigilance or warn potential intruders or thieves.