Building a treehouse - need advice on support beams

Got permission from the wife to start a treehouse project with my boys this spring. We've got a big oak tree in the backyard that's perfect. I'm planning a 6x8 platform about 10 feet up. Has anyone here built one before? Worried about getting the main support beams secured properly to the trunk without killing the tree. Don't want to cheap out on safety but also want to keep cost reasonable.