No treaty, just verbal reassurances that Russia made decisions on. This was Russia's first mistake of trusting a lying USA. When you go back in history and read the communications between the USA and Russia, you'll find the cause of the war was the NATO expansion, and the effect was Russia invading Ukraine.
Sorry, no. Russia was never promised that NATO wouldn't expand. Those "promises" were made to the Soviet Union and were never actually promised, if they had, they'd have ended up in an actual treaty. Beyond that, Russia didn't keep their promise of not attacking former Soviet Republics -- so even if the US had promised it, Russia broke the deal first, by attacking Georgia, Romania, and Tajikistan.
Also, if the war was about NATO expansion, as you claim, why did it take Russia almost 25 years after NATO had expanded before attacking? That makes no sense whatsoever, particularly as NATO had denied Ukraine membership -- there was no danger of Ukraine joining NATO until after the "rebellion" in the Donbass (which Russia supported with Russian troops and equipment) had ended, at a minimum (there were other issues, as well). And, again, since Russia was keeping that rebellion going with troops and equipment, Russia knew there was no way Ukraine was joining NATO.
Instead, this is where you need to go to Putin's writings to find the actual cause for the war, the writings where Putin talks about expanding the borders of Russia back to what they were under the Russian Empire.
Ukraine will be a neutral country as talked about in 2022, but the wamongers had to contain and weaken the hated Russis, Russia, Russia, and thousands of deaths later Ukraine will be nuetral.
Except we haven't been containing Russia. We've allowed him to attack Georgia, Tajikistan, Romania, and Chechnya, and never intervened. We allowed him to annex Crimea with little pushback. We've allowed Russia to set up a puppet government in Belarus.
As for Ukraine becoming neutral, it is sad that you think you (and Russia) should decide the internal politics of Ukraine. Ukrainians had already decided that they want to be tied to the West, not to Russia.