Flat vs curvey back? And saddle fit

What does a flat back look like vs a curvey back (but not swayed)? That probably seems straightforward but I’ve seen pictures that I though would be a flat back but was actually labeled as curvey. I would love a few pictures of both and maybe some explanation of why so that I can compare and understand. I am saddle shopping and I found one that I really love, it has everything I was looking for BUT it has a curvey tree. I ride at sale barns and ride many horses and want to know what kind of back a curvey tree is designed for so that I can make a good decision!

I have no idea how to post a picture! If you want to PM me, I could send you several examples of flat vs curvy backs and the types of saddles we use on them!