hardiness 6b/7a - planting trees (late!)

In prep for planting trees, I've started to dig out a couple of holes - I'm in southeastern PA, hardiness 6b/7a. It's getting cold - I maybe needed to do this about 2 or 3 weeks ago, but time got away from me.

So I dug this hole today - the soil is clay. super compact. really hard. Any advice on how to prep this soil to give my trees the best chance? I'm planting a bloodgood japanese maple, and a wiliting cherry, both around 5-6 ft.

Current plan is to break up that soil a bit, mix in a bit of compost (and bone meal?) then fill it in, add compost on top, and then finally mulch doughnut. I pulled out some rocks, should I drop those to the bottom of the hole to help with possible drainage issues? Anything else I should do? the ground is so compact, I'm not sure what else I should be doing.