Do you draw a card when you reveal a hidden Facebreaker during a showdown at The Dreaming Tree battlefield?

Ruling: Yes, you draw a card. The Dreaming Tree triggers when you cast a spell that chooses a friendly unit at that battlefield, which Facebreaker does (even though it also chooses an enemy unit).

Sequence:

• You cast Facebreaker from hidden at The Dreaming Tree
• The Dreaming Tree's trigger goes on the chain immediately when the spell is cast
• The trigger resolves and you draw a card
• Facebreaker then resolves with its effect

Nuances:

• The Dreaming Tree triggers as soon as you cast the spell, not when it resolves, so it works even if Facebreaker loses its targets or fizzles
• The trigger would not occur if Facebreaker is countered or defied (spell wasn't cast)
• Facebreaker no longer requires both targets to be at the same battlefield to resolve