SumDfs

public List<Tree<T>> SubTreesWithGivenSum(int sum)
        {
            List<Tree<T>> subtreesWithSum = new List<Tree<T>>();

            this.GetSubtreesWithSum(this, subtreesWithSum, sum);

            return subtreesWithSum;
        }

        private void GetSubtreesWithSum(Tree<T> tree, List<Tree<T>> subtreesWithSum, int sum)
        {
            //int treeSum = this.GetTreeSum(tree);
            int treeSum = this.GetTreeSumDfs(tree, 0);

            if (treeSum == sum)
            {
                subtreesWithSum.Add(tree);
            }

            foreach (Tree<T> child in tree.Children)
            {
                this.GetSubtreesWithSum(child, subtreesWithSum, sum);
            }
        }

        private int GetTreeSumDfs(Tree<T> tree, int sum)
        {
            sum += Convert.ToInt32(tree.Key);

            foreach (Tree<T> child in tree.Children)
            {
                sum += Convert.ToInt32(child.Key);
                this.GetTreeSumDfs(child, sum);
            }

            return sum;
        }