1 Crit (6.3%)
0% with 10-11 Atk (0+/x/x) (16%)
8.2% with 12-13 Atk (x/0+/19-) (78%)
87.5% with 14 Atk (x/x/20+) (6%)

2 Crits (0.39%)
8.2% with 10-11 Atk (0+/x/x) (16%)
100% with 12+ Atk (x/0+/0+) (84%)

Treecko 2HKO Chance: 0 + .00403 + .00331 + .00005 + .00328 = 1.07%
Treecko 2HKO Chance assuming runnable Attack: .0048 + .00394 + .0039 = 1.26%