Maybe this will help with your understanding. Posting pics when you can will also help as many experienced people here can spot what is wrong and make suggestions on what you need to do to correct it. This from McPherson Saddlery:
There are basically 5 types of trees as follows:
Full Quarter Horse: This is a tree designed to fit what is commonly referred to as the "Bulldog" style quarter horse with a back like a table top. If we were to equate it to a person, think Mike Tyson. Short, Broad Shoulders and flat wide back and therefore the bars are flatter to better fit these round-barreled horses.
Quarter Horse: This is a tree which probably fits 70%-80% of the horses out there with the exception of the narrower Thoroughbred with high withers
Semi-Quarter Horse: This is a tree which is ideal for the slimmer Thoroughbred with high withers. A horse that is built more for running (longer back, narrower chest, ribs not quite as widely sprung.
Arabian: This is a tree much like a Full Quarter Horse tree. Sometimes the only difference between the two is that the Arabian tree will accommodate a shorter back than Quarter Horses. Sometimes an Arabian tree will be even wider - more space between the bars - than a Full Quarter Horse tree. Sometimes it won't depending on the manufacturer.
"A" Fork: This tree is high in the gullet, high in the cantle and deeper in the panels and is commonly seen it what are called "Hard Seat High Back". A Wade Saddle is one of this type of saddle.
It is Important to note that the same "type" or "size" tree from different manufacturers will each fit differently. This comes about because of variations from the tree makers, the application of the woolskin and the application of the leather in the production of the Saddle which all affect the fit slightly. All horses are different and the trees are built to fit the "standard" or "average" of each breed but will not fit them all and therefore the only sure fire way to judge the fit is that each saddle must be placed on your horse's back for evaluation.