We investigate the topological complexity of non Borel recognizable tree
languages with regard to the difference hierarchy of analytic sets. We show
that, for each integer $n \geq 1$, there is a $D_{\omega^n}({\bf
\Sigma}^1_1)$-complete tree language L_n accepted by a (non deterministic)
Muller tree automaton. On the other hand, we prove that a tree language
accepted by an unambiguous B\"uchi tree automaton must be Borel. Then we
consider the game tree languages $W_{(i,k)}$, for Mostowski-Rabin indices $(i,
k)$.