Small wart on a dappled willow I just purchased
It does look like a gall and crown gall is the most common gall on Salix integra. This bacterial gall infects a wound and grows as the plant grows and becomes less uniform in shape. It could also be a nectriella fungal stem gall. You should contact the diagnostic labs at the Cornell Cooperative Extension Office of Westchester County (or your county's extension office) to have it examined.