My first choice would be to only include the public side of the tree in your tree. Don't be the one to be the revealer of the truth. You'll be blackballed from the family, and it's not worth it.
If you must save that information, keep it very very private somewhere. It's like child pornography. If anyone finds it, even a close family member, you may be in deep trouble.
If you can, leave it to your memory. And when you are old and grey, and the mood is right, maybe you can pass on the "forbidden" tales to some descendants - and they might then follow up the paper trail and fill in the research for you.