Have you tried hot chocolate made with milk and syrup?
I thought it was just a quirk of my own adhd-c kiddo (because he's a fast grower and hypoglycemic to boot, he'd wake up TOTALLY discombobulated and freaking out)... but I took care of my adhd-h nephew & adhd-i niece this summer and blam! Hot chocolate (with milk and syrup) took care of both of them as well. I don't know if it's because of the fats and proteins in the milk (we use whole or 2%) soothed the starvin'o'the'hunger... or if it was the tiny bit of caffeine in the chocolate, or the soporific effect of warm milk... but whatever it is... my SIL has now started keeping sippys of chocolate milk in the fridge ready to be zapped in her house as well.
The other 2 common adhd tricks are benedryl or melatonin. I, myself, use benedryl about 2 weeks out of every month spring, summer, and fall (I'm adhd-c, also). It's completely non-addictive... and also unlike sleeping pills doesn't last for 8 hours (lasts for 4-6), and doesn't have next day side effects since it's in and out of your system so quickly.
I use benedryl, because I have a 36 hour internal clock. The benedryl "resets" my sleep pattern enough that after a coule weeks of taking it about an hour before bed I can *typically* continue going to bed at around that hour for a few more weeks. Then I start "creeping" back upward. First night or two I'm not asleep until 3-4am, and I start resetting it at 11pm. In the winter, I don't need it, because kiddo and I are snowboarding 10 hours a day (we homeschool, so we can actually do that most days a week). We come home, shovel something into our bellies, rinse off, climb into PJs and crash.
Music played continuously at night also helps many.
I personally don't react well to melatonin (I feel cranky and hot, and never seem to all the way sleep OR wake up), so I skip the melatonin... but it works for many.
It is NOT a lack of scheduling, or anything that has to do with your parenting. So don't beat yourself up. ADHD Insomnia is just a fact of life. Especially with unmedicated adhd.