We like feasts in the Orthodox Church. We have the Prefeast, the Feast itself, the Leavetaking, and then the afterfeast. We have one of those today.
Six days after the Nativity is the Leavetaking or the Apodosis (conclusion) of the Nativity of our Lord and Savior Jesus Christ in the Flesh. On this day we repeat the liturgical rubrics of the feast itself.
Some feasts have longer afterfeasts and some actually have none. Pascha for example lasts 38 days, that leaves room for the Prefeast of Pentecost. I know it is all very confusing.
So today be bid farewell to the feast of the Nativity and prepare for the Feast of Theophany. However, the Christmas season does not end until January 6th so keep that tree in place!
Your Nativity, O Christ our God, Has shone to the world the Light of wisdom! For by it, those who worshipped the stars, Were taught by a Star to adore You, The Sun of Righteousness, And to know You, the Orient from on High. O Lord, glory to You! (Troparion of the Nativity)
Today the Virgin gives birth to the Transcendent One, And the earth offers a cave to the Unapproachable One! Angels with shepherds glorify Him! The wise men journey with a star! Since for our sake the Eternal God was born as a Little Child! (Kontakion of the Nativity)