Why does the apple trees flower develop into an apple?

Scientifically, flowers develops into fruits because the anther which stores pollen sacs that produces pollen grains will be transferred to the stigma by wind or small insects.Each pollen grain produces a pollen tube. The male reproductive cells are found inside the tip of the pollen tube.The pollen tube enters the ovule that contains an egg cell.Fertilisation occurs when the male and female reproductive cell fuses.After fertilisation, the petals,style and stigma wither and drop off but not the ovary.The ovules in the ovary start to develop into seeds and then the ovary swells up to become a fruit.