Add(remove) element(s) from an ImmutableSortedMultiset

I am struggling how to perform basic operations using a Guava ImmutableSortedMultiset...

• How would one create a copy of an existing ImmutableSortedMultiset that is contains a new element?
• How would one create a copy of an existing ImmutableSortedMultiset where one of the elements has been removed?

If possible, I would like to be able to perform these operations without sorting the existing collection each time a new element is added(removed).