https://en.m.wikipedia.org/wiki/Retrovirus

The family is characterised by its RNA genome, the conversion of single stranded RNA (their own genome) into double stranded DNA is accomplished by the reverse transcriptase which can then be integrated into the host genome by their own integrase (at random/ semi random positions) both proteins are part of the mature viron.

Other virus families based on double stranded DNA, can end up with their genome integrated randomly at double stranded breaks of the genome.