One sided bet
Q: Me and my friend were discussing about marks of a certain exam and my friend said "I won't get more than 20 marks". I said to him "You will get more than 20 marks". He said to me "If I get more than 20 marks I will give you a treat". When results came out he scored more than 20 marks. Is it permissible for me to take a treat from my friend. Is it counted as betting/gambling?