Wiktionary
n. The base on which the rest of the saddle is built. Usually based on wood or a similar synthetic material, It is eventually covered in leather or a leatherlike synthetic. The tree size determines its fit on the horse's back as well as the size of the seat for the rider.
Usage examples of "saddle tree".
Even then it was sheer bad luck that the saddle tree hit him in the stomach.
Longarm picked up his awkward load, braced the saddle tree against his left hip to leave his gun hand free, and headed north toward the engine with no further comment.
Jan took pity on him and helped him secure it to the saddle on rings embedded in the saddle tree for just such a purpose.
Since Morgan had shown no sign of being ready to go next, Duncan unbuckled his sword and hung it over his saddle tree, then headed briskly toward the shrine.
He reached down and grabbed Twoflower by the scruff of his neck dragging him across the saddle tree.
A broken saddle tree was discarded in one corner, while a lizard watched Sharpe from the curved ceiling.