Why in the given context is it "from a tree" but not "on a tree"?
Please explain with a rule or something. What's the rule here can correspond?
Boo carried the ribbon into the garden and carefully hung it from a tree
It appears to be an idiomatic usage: hang someone or something from something :
to suspend someone or something from something.
- The captain wanted to hang him from the highest yardarm as punishment. I hung a colorful decoration from the windowsill.
(McGraw-Hill Dictionary of American Idioms and Phrasal Verbs)