Vrikshasana or Tree Pose is a balancing asana. It is one of the very few standing poses in medieval hatha yoga, and remains popular in modern yoga as exercise.
Tree Pose stretches the thighs, groins, torso, and shoulders. It builds strength in the ankles and calves, and tones the abdominal muscles. The pose also helps to remedy flat feet and is therapeutic for sciatica.
Source: www.rishikeshyogsansthan.com