Start in a supine position, facing away from the tree. The head should be about a foot away from the trunk. Reach behind and grab on to the tree. Lift the legs up and bring the knees in towards the chest. Pause here for a couple of breaths. In addition to holding this stretch statically, you can also find some gentle side-to-side movement. Further, you can also practice this stretch with the arms relaxed down by the sides, or with the hands on the shins.