The accident took place yesterday when the bus heading to King's Cross in south London hit the tree near the Ship pub on Kennington Road, Transport for London officials said yesterday.
Two passengers who were trapped inside the bus had to be freed, London Fire Brigade officials said.
London Ambulance Service said it treated 32 patients in total out of which 25 people were "walking wounded" with cuts and bruises, BBC reported.
The more seriously hurt had mostly head and leg injuries, but none of them are in a life-threatening condition.
An investigation has been launched by officers from the Collision Investigation Unit but nobody were arrested yet.
