Since recognizable tree languages are closed under the rational
operations, every regular tree expression denotes a recognizable
tree language. We provide an alternative proof to this fact that
results in smaller tree automata. To this aim, we transfer
Antimirov's partial derivatives from regular word expressions to
regular tree expressions. For an analysis of the size of the
resulting automaton as well as for algorithmic improvements, we also
transfer the methods of Champarnaud and Ziadi from words to trees.