Question

how the fruits developed without fertilisation

Answer 1

In botany and horticulture, parthenocarpy (literally meaning "virgin fruit") is the natural or artificially induced production of fruit without fertilization of ovules, which makes the fruitseedless. ... In some plants, pollination or another stimulation is required for parthenocarpy, termed stimulative parthenocarpy.

Answer 2

Fruits can also develop without fertilisation by parthenogenesis by injecting some growth regulators and others this process is done in such plants which bear a very small seed, banana is a parthenocarpic fruit.