Tree with brown leaves

The leaves on this tree suddenly turned brown and started falling off. There are still a few green leaves. I think it might be an oak tree (?)

Does it have some kind of disease, or does it just need more water? This tree was planted last year, and there's another one that is still green and full of leaves.

Thank you :)

 

Pin Oak. It's growing in a very tough environment for a tree; extra water and mulch would help.

 

Thank you! Will do.