Is there any way to transition to a sub-state machine through script?

I have made a state behaviour that selects a random animation and transitions to it. The problem is I can't crossfade to the sub-state machine with Animator.Crossfade(), because it says "State could not be found". I've tried to add an empty state and then transition to the substate but it creates a delay.

Is there any way to play a substate machine through script?