Tree of knowledge
The Tree of the Knowledge of Good and Evil is, according to the Bible, a tree that God placed in the center of the Garden of Eden. Eating its fruit gave one knowledge of good and evil. This is contrasted with the idea that Adam and Eve were created without such knowledge. The problems associated with the tree are discussed along with original sin.
The Tree is often described as an apple tree, and so apples are often used as symbols as sin or temptation. The original myth, however, makes no reference to what specific fruit grew on the tree.