Mr. MacBain, in vol. xiii of the Celtic Magazine (pp. 213 et seq.), and since reprinted in Celtic Fairy Tales. I give below a summary of the tale, "Gold-tree and Silver-tree," with the more important passages in full.
Silver-tree, the wife, is jealous of Gold-tree, the daughter; she consults a trout in a well as to who is fairest, and learns it is her daughter, whereat she takes to her bed, and declares one thing alone will heal her, her daughter's heart and liver. A he-goat's heart and liver are given her, and Gold-tree is sent off secretly and married to a foreign king. After a year Silver-tree consults the trout again, and learns that her daughter is still alive. She sets sail for the foreign land, and kills Gold-tree with a poisoned stab in her finger; but so beautiful did Gold-tree look that her husband would not bury her, but locked her in a room where no one would get near her. "After a while he married again, and the whole house was under the hand of this wife but one room, and he himself kept the key. One day he forgot the key, and the second wife got into the room. What did she see there but the most beautiful woman she ever saw." Taking the poisoned stab out of her finger, Gold-tree rose alive as beautiful as she was ever. At the fall of night the prince came home downcast. "What bet," said his wife, "would you put to me that I would make you laugh?" "Nothing could make me laugh, save Gold-tree to come alive." "Well, you have her alive down there in the room!" When the prince saw Gold-tree, he began to kiss her and kiss her and kiss her, so that the second wife said he had better stick to her and she would go away. "No," said the prince, "indeed you will not go away, but I shall have both of you." It is then told how the wicked Silver-tree is punished, thanks to the second wife, and the story winds up with "the prince and his two wives were long alive after this, pleased and peaceful, and there I left them."
It is hardly necessary to set out all the interesting points of contact between this and other versions of the Snow-White formula, as well as between it and the Breton lai.