Basically, yes - branches are chosen with probabilities proportional to their weights, but you can achieve that with just one random float. Just pick a random

Basically, yes - branches are chosen with probabilities proportional to their weights, but you can achieve that with just one random float. Just pick a random x from [0, sum of weights in the tree], then find a node n, such that sum of weights S to the left of n is no more than x and S+weight(n)>=x.