I made a sketchbook.
The design is loosely based on Yggdrasil, the world tree from Norse myth.
The Apple doesn’t really factor in as part of the world tree mythos, but it represent the golden apples of Idunn, which granted the aesir their eternal youth.
The dragon is Nidhogg, who gnaws at the roots of the world tree, and the corpses of those guilty of murder, adultery, and oath-breaking.
The squirrel is Ratatoskr, who runs up and down Yggdrasil carrying messages between Nidhogg, who dwells beneath the roots, and the Eagle, who perches on the branches of the great tree.