How set, append, insert new value in NSSet in Swift?

Question

How to add dynamic value in NSSet variable?

var productID: NSSet = NSSet(objects: "com.b100bios")

append, add new value in productID "new 1","new 2", "new 3" in Swift.

expected result: productID = {("com.b100bios","new 1","new 2", "new 3")}