Solution Review: Finding Nodes at "k" Distance From the Root

using System;
namespace chapter_6
{
    class Solution
    {
        //Helper recursive function to traverse tree and append all the nodes
        // at k distance into result string
        static void findK(Node root, int k, ref string result)
        {
            if (root == null)
                return;
            if (k == 0)
            {
                result = result + root.value.ToString() + ",";
            }
            else
            {
                //Decrement k at each step till you reach at the leaf node
                // or when k == 0 then append the Node's data into result string
                findK(root.leftChild, k - 1, ref result);
                findK(root.rightChild, k - 1, ref result);
            }
        }
        static string findKNodes(Node root, int k)
        {
            string result = string.Empty;
            findK(root, k, ref result);
            return result;
        }
        static void Main(string[] args)
        {
            BinarySearchTree BST = new BinarySearchTree(6);
            BST.insertBST(4);
            BST.insertBST(9);
            BST.insertBST(5);
            BST.insertBST(2);
            BST.insertBST(8);
            BST.insertBST(12);
            Console.WriteLine(findKNodes(BST.getRoot(), 2));
        }
    }
}