The apple doesn’t fall far from the tree - children are like their parents. 

One bad apple spoils the barrel - just one person or thing can ruin a situation, group, etc. 

The apple of my eye - a favourite or cherished person. 

Comparing apples and oranges - two things which cannot be compared, since they are so different. 

As American as apple pie - having characteristics that are quintessential of a certain country.