I was just playing around on the grass the other day and upon reviewing the video I decided to show this part because it’s not too difficult and an interesting hip opener yet I don’t see it done too often. Doing the whole sequence with your foot like that forces you to engage your core in a different way and opens your hips up in the process.
If you never tried this before, just hang out in side plank (vashistasana) with your foot on your inner thigh, just like you would in tree pose. If you can’t get your foot above the knee, put it on your lower leg instead. Just don’t rest your foot ON the knee because pressure on the knee joint in that position isn’t a good idea. Either have your foot be on your inner thigh or lower leg, but not on the knee. (These alignment-safety-tips apply to the regular ol’ standing-tree-pose.)