* Bussing: This spelling refers to the action of transporting people, especially in a large vehicle. For example, "school busing" or "bussing passengers to the airport".
* Busing: This spelling is the more common spelling in American English and refers to the act of washing dishes. For example, "I have to do the busing tonight".
The spelling "bussing" is more common in British English, while "busing" is more common in American English.
The best way to choose the correct spelling is to consider the context and the intended meaning.