Since the MM;s are not brokers but are dealers then they take a risk ( principal) position in the shares as such they have bought from you and sold to someone else and that will be two trades.

Simple case suppose you sell 10000 at 4pm on day1 and the MM sits on it

overnight and then teh next day the MM sells to someone else.

Would not  both cross as distinct transactions 10kon day1 and 10 k on

day 2

Soif they happend same day then same trades and teh voulume 

wil be 20k