Sugar Maple (abnormal growth)

Galls can be caused by fungi and insects. Burls can be caused by stress or injury. On branches and stems, both galls and burls result in modified wood tissue due to excessive cell division and enlargement. Although peculiar, galls and burls will not harm the tree, while removing them could cause a tree wound that could eventually be harmful to tree health. Your best bet is probably to leave the growth alone.