Why sum is not 6 with this parallel algorithm

Why sum is not 6 with this parallel algorithm

/*
            integer  B[1..n]
            forall i in 1 : n  do
                B[i] := ai
            enddo
            for h = 1 to k do
                forall i in 1 : n/2^h do
                    B[i] := B[2i-1] + B[2i]
                enddo
            enddo
            S := B[1]

            */
            int n = 3;
            int[] hello = new int[n+1];
            int[] B = new int[n+1];
            hello[0] = 0;
            hello[1] = 1;
            hello[2] = 2;
            hello[3] = 3;
            //hello[4] = 4;
            //hello[5] = 5;
            Parallel.For(1, n+1, ctr => { B[ctr] = hello[ctr]; });

            for(int h =1; h<=3; ++h)
                Parallel.For(1, Convert.ToInt32(n/Math.Pow(2,h)), ctr => {
                    //if (2 * ctr - 1 >= 0 && 2 * ctr <= n)
                        B[ctr] = B[2 * ctr - 1] + B[2 * ctr]; 
                    //else if(2 * ctr <= n)
                       // B[ctr] = B[2 * ctr]; 
                });

            int sum = B[1];
            Console.WriteLine(sum.ToString()); 

---

bots