treat (someone or oneself) to (something)
To pay for or provide something to someone or oneself as a special gift or treat. She treated all the kids to ice cream after the movie. I decided to treat myself to a nice meal after getting such a good result on my exam.
treat someone to something
to provide and pay for something for someone as a gift or as entertainment. I will be delighted to treat you to dinner. After the play, they treated themselves to pie and coffee.
To provide someone with some food, entertainment, or gifts at one's own expense: She treated her brother to dinner and a movie. I treat myself to a day in the country once in a while.