when a>3, 40% probability output 4, 60% probability output 5
> 3
4(0.4), 5(0.6)
whern a<= 3, 20% probability output 4, 80% probability output 5
<= 3
4(0.2), 5(0.8)
when b=4, 30% probability output "label1", 70% probability output "label2"
4
< 0.3
label1(0.3), label2(0.7)
when b=5, 50% probability output "label3", 50% probability output "label4"
5
< 0.5
label3(0.5), label4(0.5)