Thanks everyone.
You are right Hans, the distortion bothers me as well but I don't know how to do better. It is mostly and effect of perspective. The angle of view is quite large and there has to be some kind of projection. I have used a spherical projection here. Any idea on how to improve?
Paco, thank you for the detailed review! Indeed, there are blown out whites and I could have done better. I was trying to push the contrast as much as I could and there are collateral damages...
Akira: yes, it is a combination of 7 shots (only!). It is amazing to see what decent stiching software can do with such messy images. there are so many branches and yet the final image looks OK to me with not much work done (by me).