The trees used by The National Saddle Centre are wooden laminated spring trees, made in England to exacting standards. The wooden and resin rigid and semi rigid trees, whilst robust, have no "give" and are harder on the horse's back. To compensate for this rigidity a large large, deeply flocked panel is needed to protect the horse's back and this is not often the choice of the educated horseman.
Other saddle makers use synthetic trees, and composite molded trees which have no channel and as such there is increased danger of direct pressure on the spinous processes. We find that such trees whilst they are far cheaper to produce do not offer the rider the "feel" and the lighter they are the more they are liable to twisting and torsion.
The trees below are both used in our saddles, tree A is used in the Aotearoa Standard Seat Dressage saddle and tree B is the one we are using in the Aotearoa FBK Dressage saddle.
It is not difficult to imagine that tree A is more suitable for the horse with higher withers and a greater curve in the back and tree B suits the wider, flatter backed types. Both of these trees are our standard medium wide and neither are designed for extreme conformation problems although with different panels and rear gussets provide good, comfortable and balanced fits on many horses.