public int subtree_size(int index)
{
int count = 1;
if (this.Nodes[index].Child1!=-1){
count += this.subtree_size(this.Nodes[index].Child1);
}
if (this.Nodes[index].Child0!=-1){
count += this.subtree_size(this.Nodes[index].Child0);
}
return count;
}