Loosen the leg straps up a little bit. Reposition the saddle so your weight is in the saddle not in the legs straps. Your knees shouldn’t really ever be nipple high. Like others have said, tether at nose height or head height, length of bridge and tether to put your knees slightly above 90 degree. That will have you leaning maybe 20 deg from straight up and down. Starting out I think a lot of people thing you’re supposed to be dang near horizontal, but just a slight lean back is going to give you a good mixture of stability, comfort, and ability to maneuver around the tree. Too short or not high enough and you’ll be extremely close to the tree and stable, but your maneuvering will decrease (won’t be able to move around the tree). Conversely, a long and high bridge will give you too much maneuverability with decreased control and stability (feels like a swing). Find your happy medium, but first, loosen those straps on your boys.
Finally, a tight waist belt is more important than the legs, though the legs are not unimportant. I wear a tight belt, a little less than snug on the legs.