ABC News December 12, 2017

5-year-old decorates tree each Christmas for heart donor

WATCH: 5-year-old dedicates tree each Christmas to heart donor

Decorating a Christmas tree is the highlight of the holiday season for many 5-year-olds. For a very meaningful reason, little Mallory Kate Hall decorates two.

The kindergartner from Cumming, Georgia, was the recipient of a heart from an anonymous donor, transplanted to her body in December 2014 at Children's Healthcare of Atlanta. Since then, the family has a second tree to represent the life of her organ donor. Mallory hangs an ornament on this tree each year.

The tree has four ornaments: one Mallory received while she was waiting for her transplant and then three more, one hung each year on the anniversary of her transplant.

"We've always said that since we've received this gift, her heart, we were no longer a family of four but a family of five," her father, Dustin Hall, said.

Mallory knows she was given a gift and that her heart is very special, her mother, Jessica Hall, said, but she doesn't yet realize it came from another person.

Her father was in the hospital with Mallory the night they got the call she would receive the new one she needed. After calling his wife and other family members, he woke Mallory from her sleep and took a stethoscope so he could hear her heart one last time. "It would be the last time it would be that heart," he said.

"To make a selfless decision to give a little girl a chance at life," Jessica Hall said. "We do our best to honor that family, that child. That little boy or little girl lives in Mallory."

And each year, when her heart anniversary comes around and it's time for Mallory to add an ornament to the tree dedicated to her donor, the family once again reflects on what Christmas is all about.

"I think it [the anniversary of the heart transplant] gets right to the heart of Christmas," Dustin Hall said. "It's about families being together and what you share. That's what love it. There's someone who doesn't have that, but they do have the knowledge that many lives were changed. Something that wasn't good, something good came out of it."

The heart transplant, Dustin Hall said, is for his family "the gift that keeps giving for us."