The tree in the title grows in tenement districts, without water or light, even without soil. It symbolizes perseverance and hope amidst hardship. The tree is a recurring symbol throughout the novel; when Francie is born, Katie explicitly likens her life to the tree's. Katie knows she will keep living, no matter how sick she becomes. In Brooklyn, this tree trumps all others. When Neeley and Francie bring home a small spruce to nurture, it dies even as they try to take care of it. But the tree keeps on. The reader should think of the tree not only in terms of Francie, but also the poor community as a whole. It "likes poor people." When Francie leaves Brooklyn at the end of the book, Florrie Wendy symbolically takes her place. The tree grows for Florrie, too, as it must have for Flossie Gaddis before Francie.
Francie sees the Tree of Heaven every single day; it is a touch of beauty in her daily surroundings. When Francie looks down from the fire escape, it looks like the tops of many green umbrellas. It makes sense that Smith would choose an object with which Francie is totally familiar. Here again, the author shows how one may view small, material objects differently. It is not a special tree, in a conventional sense; it grows everywhere where there are poor people. It is not grandiose like the sea or a majestic mountain. It is humble, and its humility makes it all the more powerful.