Does the Doppelganger apply bonus damage from it’s Surpise Attack feature twice?

The Doppelganger gets extra damage if it surprises an enemy and hits it.

Surprise Attack. If the doppelganger surprises a creature and hits it with an attack during the first round of combat, the target takes an extra 10 (3d6) damage from the attack.

Since the Doppelganger gets 2 attack per round, if it hits with both attacks during the first round, will it add the bonus damage on each attack?