Answer:
The narrator is remarking that trees make the night darker.
Step-by-step explanation:
Allen Ginsberg was an American poet. He wrote the poem "A Supermarket in California" in 1956 that was first published in Howl. In the poem, the narrator visits a supermarket in California where he imagines himself following Walt Whitman who was shopping in the supermarket of California.
The meaning of this phrase ''The trees add shade to shade'' means the narrator is remarking that trees make the night darker.