It's the title of the Longfellow poem that begins, "Under the spreading chestnut tree"
... 
From the start, he held himself to the highest literary standards, and was ... of the 
Hesperus, the village blacksmith under the spreading chestnut tree, the... [DOC] [TLE] mudcat.org: Lyr Req: Under the Spreading Chestnut Tree [PAR] The title boxes on here are too short!