What causes fuel in oil honda four wheeler?

I have a four wheeler Honda TRX350D Foreman 4x4.
Would turn over but not start.
Checked oil and it had gas in it. Drained and put in new oil.
Checked fuses and tinkered with fuel pump.
It now starts and runs but I don't want to use it until I resolve
'oil in gas' problem.
Would fuel pump going bad cause the gas/oil problem?
Would there be a more reasonable reason for this?

if its injected the injectors could be worn out and leak into the cylinder after its shut off, then go by the piston an into the crankcase

if carbureted, can leak out of the float bowl when shut off and dot the same thing.

if it has a fuel shutoff valve, always shut it off when not running or this can happen regularly.

hope this helps