All the years I lived in the maritimes (eastern Canada) I never heard of this Christmas tree story. In 1917 a ship loaded with explosives drifted into the Halifax harbour while it was on fire. A mass explosion occurred killing many and injuring hundreds if not thousands and demolished the area close to the harbour. The good people of Boston sent immediate aid to Halifax by way of doctors,volunteers clothing food money and more. The city of Halifax was left with a never ending gratitude to the people of Boston and has for many years sent a giant Christmas tree as a token of their appreciation.
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