Tree pose, or Vrksasana, is a very grounding pose. This pose can be done with one hand on the wall or a chair to help with balance.
To begin, place both feet hip width apart, inhale deeply and send energy down through your feet, emphasizing a feeling of "rooting" into the ground or floor.
Slowly shift your weight into right foot and use your left hand to reach down and assist you in placing your left foot somewhere on your right leg. It doesn't matter so much where you put your foot, as long as it is not on your knee or causing you any sharp, shooting or pinching pains.
The only requirement for this pose is to lift the left foot off of the floor. If you can, place the foot as close to your groin as possible.
To help with balance away from the wall, place the hands on the hips or stretch them out into a "T" shape.
If you feel well-balanced, lift the arms up over the head as seen in the picture, just as a tree reaches up towards the sun.
Hold the pose for 5-10 breaths, focusing your gaze on a point in front of you (your "drishti") to help maintain balance.
If you sway a little bit or fall over, don't worry. The most supple and strong trees bend in the wind.
Source: Asheville Yoga