Some traditions hold the apple to be the gift of Divine wisdom and immortality. The fruit of the tree of life. In Celtic myth the golden apples kept the Gods and Goddesses young and brought them wisdom.
In fables such as Sleeping Beauty, we see the apple again as a symbol of wisdom but in this case the evil queen is offering a tainted apple to the young heroin, a metaphor for nieve acceptance of flawed knowledge and so she falls into a long sleep (is lost to the world until pure love revives her).
An apple a day keeps the doctor away stems from " Eat an apple on going to bed, And you'll keep the doctor from earning his bread." a phrase used as late as the mid 19th C which originates in the ancient belief that the mythological apples kept the gods immortal which, I dare say may have come from our ancestors discovering that storing apples and eating them over winter kept them healthy.
A ladder suggests making an effort to gain something, nourishment in the form of knowledge or understanding but it feels shakey and unsafe which suggests that you don't quite trust or have faith in something which you are trying to figure out.
