We’re not adding fingers or apples. We’re adding quantities. I am making a distinction between a symbol (1) and the thing it represents, namely, as many of something as you can indicate with a single finger. Could be a single marble, apple, planet, whatever. I chose fingers because they are a very common way to signify this abstract thing that is quantity.
One and one of something will always equal the quantity symbolized by two fingers. But it will not always equal “2” or a mark named “two” because that is a symbol and not a number. “2” is not a number. It’s a symbol. The quantity is the number, and I showed it instead of naming it because the name is the symbol.
I’m giving the same answer that @GeorgeGee gave, and adding an explanation. It has nothing at all to do with personal relationships or the irregularities of fruit. It is about the abstract idea of number and the different ways it’s symbolized, depending on the base you are counting in.
In base 2 you count like this:
1 10 (this is the base)
11 100 (this is the square of the base)
101 110
111 1000 (this is the cube of the base)
In base 6 it’s like this:
1 2 3 4 5 10
11 12 13 14 15 20
21 22 23 24 25 30
31 32 33 34 35 40
41 42 43 44 45 50
51 52 53 54 55 100
etc.
Here “100”—the square of the base—is equal to 36 in base 10, which is 6×6.