If you feel that Yoga may not be challenging enough for your already rough and tough routine I can tell you that there are certain forms of Yoga that will help you build even better. The above pose is a modification of the headstand and is much easier on your shoulders and head. I much prefer it and I can do this pose on my papasan.
On the tree pose above I like to bring the leg all the way across the opposing leg and up to increase the flexibility challenge for the knee. For the upper body I bring the praying position for the hands all the way above my head to challenge my core muscles. This will also challenge your balance in this pose which is crucial in all the standing poses. Don't forget to breathe in regular, long intervals.
With much love and support for your success,
The Castle Lady