struct tree{int value; struct tree *left; struct tree *right;};
struct tree* find(int ans, struct tree *current){
　struct tree* temp;
　if(current == NULL) return NULL;
　if(current->ans == value) return current;
　if(temp = find(ans, current->left) != NULL) return temp;
　return find(ans, current->right);
}

きっと、自分で検索した方が早いです。