  CCS can be considered as a most natural extension of finite state automata in
which interaction is made possible thanks to parallel composition. We propose
here a similar extension for top-down tree automata. We introduce a parallel
composition which is parameterized by a graph at the vertices of which
subprocesses are located. Communication is allowed only between subprocesses
related by an edge in this graph. We define an observational equivalence based
on barbs as well as weak bisimilarity equivalence and prove an adequacy theorem
relating these two notions.
