Answer :
If the trees are on a person's property and you don't ask them if you can post a flyer on it then it is illegal. you have to ask the person who owns the house of the doorsteps to put a flyer on their doorstep. if you don task them and do it, it is illegal. if they say yes, then it would be legal. Does this help?
You will have to ask permission if you could put the poster there.