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According to the National Park Service, the General Sherman tree is the largest tree in the world (though not the tallest).
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By contrast, the General Grant comes in 3rd just ahead of the Lincoln tree. But Grant's tree has other distinctions. For one, it's the National Christmas Tree. Bet you didn't know that. For another thing, it's a shrine to service men and women. Quoting the NPS web site linked above, "the General Grant Tree is a living memorial to the men and women of the United States who have given their lives in service to their country. It was proclaimed a National Shrine on March 29, 1956 by President Dwight D. Eisenhower. The official dedication was made that year on Veterans Day, November 11, by the president's personal representative, Fleet Admiral Chester Nimitz."
The Robert E. Lee tree, on the list of the 30 largest Giant Sequoia, ranks a respectable 12th (named during Reconstruction, five years after Lee's death). See a photo here.
As an aside, the General Sherman apparently started out as a Communist tree. Quoting Wikipedia (at my peril), "The utopian socialist community Kaweah Colony first identified it as the largest giant sequoia and named it after Karl Marx. The National Park Service later renamed it." To those miners who named the Alabama Hills, I'm sure it hardly seemed an improvement.