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maybe even pvc.

Since your brought that up, I had a crazy idea about a TELESCOPING pole set-up using PVC pipe?
Not sure IF the dimensions would work-out but here it goes
Take 2 lengths of PVC pipe, say 3/4 and 1 inch. Idea being 3/4 will sleeve into the 1 inch? Then drill a hole EVERY foot thru BOTH pipes that you can fit a CLEVIS type pin thru. Just decide the longest length you'd want and how much the need to overlap to keep structural integrity? On each end you drill a small hole on each unit so you can use a hooked bungee cord to set height on trees. Then secure with flat strap like Westwood did.  The address any issues that might come up after you get the intial set-up.

IF that thought worked out, I'd take a step drill and figure out a pattern and HONEYCOMB the two sliding sections to lighten weight. You could easily lash the telescoping pieces one each side to thwart/yoke.

Schedule 40 pipe is tough stuff and you don't have to worry about it cracking/splitting like wood can.

You could do the same with round or square aircraft grade aluminum but it would cost a lot more.