It’s literally what the song says. On the first day, I got a partridge in a pear tree. On the second day, I got 2 turtle doves and a partridge in a pair tree.
If you think the gifts weren’t given recursively it’s because you believe it should be that way, not because you’re paying any attention to the lyrics as they’re written.
As of this comment, I’m guessing the 3 people who down-voted this post do.