Ghyakulla and Khuushoi are Sister goddesses. The land, as you know, is rich and fertile, full of the promise of life and good harvests. Winter is cold and sterile; nothing grows but the evergreens. So you see the natures of the two sisters. Ghyakulla had a son, a bright, loving child whom she cared for more than anything. Khuushoi was sterile, could bear no cubs, and in her winter fastness, she became jealous.
Khuushoi stole the child and took him down to her underground palace of snow and ice. Ghyakulla was beside herself with grief because she didn't know what had happened to him. She began to search frantically. It was the middle of winter, and no one had seen the child taken. All the animals and birds were huddled in their burrows and nests keeping warm or hibernating till the spring. All the trees were asleep, except those you see here— the evergreens. Ghyakulla asked each one in turn if they'd seen her son, but they were afraid of Khuushoi and lied, saying they'd seen nothing. Save for one. The snow tree.
It told Ghyakulla in a trembling voice what had happened and explained its fear that Winter and her frost demons would destroy it for telling her.
Ghyakulla promised the tree that it wouldn't suffer for helping her, and as a sign of her gratitude, she turned the underside of its leaves white and showed it how to hold the pale side up to the sky, so it would be unseen by Khuushoi and her demons.
The tears of gratitude she shed on the bush also turned its green berries to the brightest red of any in winter. That's why it's called the snow bush, and its berries, the Tears of Ghyakulla.
Then she set off for her sister's palace. Khuushoi, alerted by her demons, tried to hide the way to her palace by covering the world in a blanket of snow. Every step of the way, her sister sent demons to hound Ghyakulla, but the power of the land is greater than that of winter and eventually, Ghyakulla reached the palace. There she confronted her sister.
Khuushoi was prepared to fight it out, but not Ghyakulla. She understood the loneliness that had prompted her sister's act and offered a compromise.
So Vartra visits Khuushoi for four months of the year. During that time, Winter, or Khuushoi, reigns and nothing will grow till Vartra is returned to his mother.