这里以层序插入二叉树的结点，以先序遍历输出。

上一篇关于二叉树的内容在这里：https://lovedm.club/?id=110

using System;
using System.Collections.Generic;

namespace BTree
{
    class Program
    {
        static void Main(string[] args)
        {
            Tree tree = new Tree(new Node(10));//           10
            tree.InsertNode(new Node(9));      //          /    
            tree.InsertNode(new Node(8));      //         9    8
            tree.InsertNode(new Node(7));      //       /    /  
            tree.InsertNode(new Node(6));      //      7   6 5    4              
            tree.InsertNode(new Node(5));      //     /  
            tree.InsertNode(new Node(4));      //    3
            tree.InsertNode(new Node(3));      //

            tree.PreTraversal(tree.root);
            Console.WriteLine("--------------");
            tree.LevelOrderTraversal(tree.root);

        }
    }

    /// <summary>
    /// 树的节点
    /// </summary>
    class Node
    {
        public int Value = 0;
        public Node Left;
        public Node Right;
        public Node(int value)
        {
            Value = value;
        }
    }

    /// <summary>
    /// 二叉树
    /// </summary>
    class Tree
    {
        public readonly Node root;
        public Tree(Node node)
        {
            root = node;
        }

        /// <summary>
        /// 以层序进行插入结点
        /// </summary>
        /// <param name="node"></param>
        public void InsertNode(Node node)
        {
            //使用队列
            Queue<Node> queue = new Queue<Node>();
            //首先根节点入队列
            queue.Enqueue(root);
            //队列不为空一直循环
            while (queue.Count != 0)
            {
                //出队列
                Node tempNode = queue.Dequeue();
                //左孩子不为空，那么将左孩子进队列；如果左孩子为空，则将结点挂到左孩子
                if (tempNode.Left != null)
                {
                    queue.Enqueue(tempNode.Left);
                }
                else
                {
                    tempNode.Left = node;
                    return;
                }
                //右孩子不为空，那么将右孩子进队列；如果右孩子为空，则将结点挂到右孩子
                if (tempNode.Right != null)
                {
                    queue.Enqueue(tempNode.Right);
                }
                else
                {
                    tempNode.Right = node;
                    return;
                }

            }
        }

        /// <summary>
        /// 先序遍历
        /// </summary>
        /// <param name="node"></param>
        public void PreTraversal(Node node)
        {
            if (node == null)
            {
                return;
            }

            Console.WriteLine(node.Value);
            PreTraversal(node.Left);
            PreTraversal(node.Right);
        }

        public void LevelOrderTraversal(Node node)
        {
            Queue<Node> queue = new Queue<Node>();
            queue.Enqueue(node);

            while (queue.Count != 0)
            {
                Node tempNode = queue.Dequeue();
                Console.WriteLine(tempNode.Value);
                if (tempNode.Left != null)
                {
                    queue.Enqueue(tempNode.Left);
                }
                if (tempNode.Right != null)
                {
                    queue.Enqueue(tempNode.Right);
                }
            }
        }
    }
}