The Tree by the Woodpile

I look at that old tree again, from top to bottom, from side to side and then slowly walk around, not sure what I am looking for. It is a riddle to me. Grandmother looks at me and smiles. She motions for me to come beside her and then she says, “You see, my boy, the moose eats the leaves of that tree and we eat the moose, so that is our food!” I understand at once, but she continues. “Do you see that nest in the tree? It is the home of the robins and it gives them shelter. Also, the squirrel lives there and he lives on the seeds of the tree, so it is his food.”