I had a similar tree issue like yours about 5 years ago, I compounded the issue by trying to drop another tree into it figuring it would knock it loose, It knocked the first tree down, but the second tree got hung up in the same spot, (both trees were full mature 75' black birch W/ 20 -24" bases) my dad and I stood there scratching our heads trying to figure out the next step when the old timer neighbor stopped by. He saw the problem and said let me teach you something , he grabbed the saw and made a cut on the leaner about 5' in the air an angle, then he went a couple feet lower and made another angle cut in the opposite way, he then made a plunge cut on his bottom cut but left 2 strips of uncut wood on both sides, he said grab an axe and hit here, which I did, it caused the cuts to collapse inward and the log to drop down, the rest of the tree followed. I asked him how he knew that and his reply was " I've been burning wood for 70 years, we always took our own tree's down, and we don't waste them" after the tree was down he went back home, probably laughing at us under his breath, he was in and out in less than 5 min