u/Exotic_Interview6013

I'm looking into building an a-frame for a slackline swingset for my daughter. I originally was thinking of doing two 12' 6x6 posts and putting them 4-5 feet in the ground with cement, but I'm worried it will not be stable enough. And in order to stabilize it, I'd need to anchor it so it seems quicker and easier to just build an a-frame. My question is, what size lumber would you recommend? Ideally, I'd like the top of the line to be ~6 feet off the ground. I've gotten a little overwhelmed by all the info online, so I'm hoping someone here can help?

Thanks!