Preorder Tree Traversal - using stack - iterative solution

PreorderTreeTraversal_UsingStack.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace preorderTraversal
{
    public class TreeNode
    {
        public int value { get; set; }
        public TreeNode left { get; set; }
        public TreeNode right { get; set; }

        public override string ToString()
        {
            return value.ToString();
        }

        public TreeNode(int v)
        {
            value = v;
        }
    }

    class Program
    {
        

        static void Main(string[] args)
        {
            TreeNode node1 = new TreeNode(1);
            node1.left = new TreeNode(2);
            node1.left.left = new TreeNode(3);
            node1.left.right = new TreeNode(4);
            node1.right = new TreeNode(5);
            node1.right.left = new TreeNode(6);
            node1.right.right = new TreeNode(7);

            List<TreeNode> preorderNodes = preOrderTraversal(node1);
            TreeNode[] arr = preorderNodes.ToArray(); 

        }

        /*
         * 1. Manually review each line, each variable in the function, make it best; 
         * 2. Go over a test case, and do some static analysis, execute the code manually. 
         * go over the tree with value 1 - 9, and then, make sure that 
         * the output will work exactly the correct order. 
         * 
         *          1
         *      /     \
         *      2      5
         *    /  \    /  \
         *    3  4   6   7 
         *    
         * preorder: 1 2 3 4 5 6 7
         * 
         */
        public static List<TreeNode> preOrderTraversal(TreeNode root)
        {
            if (root == null)
                return null;

            List<TreeNode> preOrderNodes = new List<TreeNode>();

            TreeNode runner = root;

            Stack<TreeNode> stack = new Stack<TreeNode>();

            stack.Push(runner); 

            while (true)
            {
                if (stack.Count == 0)
                    break;

                runner = (TreeNode)stack.Pop();
                preOrderNodes.Add(runner); 

                if(runner.right != null)
                    stack.Push(runner.right);

                if (runner.left != null)
                    stack.Push(runner.left);                 
            }

            return preOrderNodes; 
        }
    }
}