Hanging a Tree Swing
I would not use any type of bolt through the branch.

i would use a rope or, better, a strap to make a collar around that branch and another around a branch behind to share the load, which will give ample support. Think of those 2 or 3" wide loading straps and then use a D-link to attach the swing to the strap, that way you won't damage the tree.

You could esily brace to two other branches...