Brebby, the Loyal Doggo

Brebby, the Loyal Doggo enters the battlefield with two +1/+1 counters on him.
Whenever a green creature you control gets +1/+1 counters, put that many counters on Brebby, the Loyal Doggo, then if Brebby has five or more +1/+1 counters, put a trample counter on Brebby, the Loyal Doggo.