Task trees are common notations used to describe the interaction between a user and an interactive application. Thus, they contain valuable information about the expected user behaviour. In this paper, we present a method for automatically generating test data from a task tree. The task tree is extended to support operational profile specification. The user behaviour is automatically extracted as a probabilistic finite input-output state machine, according to formal semantics defined for this purpose for the task tree operators. Based on previous work on testing interactive applications by means of the synchronous approach and the Lutess testing environment, we show that this model can be used to generate test data simulating the user behaviour.