Are you looking to add a separate animation for a double jump as well? You might find this tutorial useful: https://www.youtube.com/watch?v=n7MaVJy76Gw
FoozleCC on YouTube does a great job, explaining how to create a state machine for a platforming game. I've used this for my current project, and have heavily modified it, and expanded upon the foundation he teaches in this tutorial.
I'm not exactly sure what you are asking, but you might find an answer there. I think you want a separate animation, or frame, for the apex of the jump. For this you would need to track the players Y position. From where it begins the jump, then when it reaches roughly the maximum height(depending on your platformer behavior preferences), and change state and/or animation when it reaches that Y position in relation to where it began before the jump.
An easy way to do this may be to have both animations, all within the jumping animation. Then set it to not be a looping animation. So it's timed to play the beginning jump animation, through to the new animation at the top of the jump then stop playing. Then, switch to the falling animation while falling.
Not sure if any of this helpful. It's early here, and I'm still waking up XD. Not sure how much help I'll be today, as it's a busy one. But, I'll try to check back here and there if you're around.