Oh, I totally cheated and just bought a seedling. I'm very hit and miss when it comes to getting trees/seeds to sprout.
I think out of 100s of empress seeds I've tried, I've had 2 germinate. So much for invasive.
I thought about buying a seedling, but they were too costly for me at that time. I think I got 50 or 100 seeds. But so far nothing.
I also bought an empress tree. It is now over 30' tall. And every other year it drops seeds and a few of them sprout. I can see where it might be an invasive species. But its a great shade tree and the blooms a quite pretty.