Clove hitch and a half hitch (just in case) on one end around the tree and as John Fenna says a round turn and two around the other tree. This will get your line nice and tight.
The clove hitch will not come undone and the round turn is a knot that can be undone under tension. Both go around twice so ease the strain on the tree and line.
Swyn.
The clove hitch will not come undone and the round turn is a knot that can be undone under tension. Both go around twice so ease the strain on the tree and line.
Swyn.