完善所以c#相关的文档和代码

codes/csharp/chapter_tree/binary_tree.cs

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+using hello_algo.include;
+using NUnit.Framework;
+using System.Collections.Generic;
+
+
+namespace hello_algo.chapter_tree
+{
+
+    public class binary_tree
+    {
+        [Test]
+        public void Test()
+        {
+            /* 初始化二叉树 */
+            // 初始化结点
+            TreeNode n1 = new TreeNode(1);
+            TreeNode n2 = new TreeNode(2);
+            TreeNode n3 = new TreeNode(3);
+            TreeNode n4 = new TreeNode(4);
+            TreeNode n5 = new TreeNode(5);
+            // 构建引用指向（即指针）
+            n1.left = n2;
+            n1.right = n3;
+            n2.left = n4;
+            n2.right = n5;
+            Console.WriteLine("\n初始化二叉树\n");
+            PrintUtil.printTree(n1);
+
+            /* 插入与删除结点 */
+            TreeNode P = new TreeNode(0);
+            // 在 n1 -> n2 中间插入结点 P
+            n1.left = P;
+            P.left = n2;
+            Console.WriteLine("\n插入结点 P 后\n");
+            PrintUtil.printTree(n1);
+            // 删除结点 P
+            n1.left = n2;
+            Console.WriteLine("\n删除结点 P 后\n");
+            PrintUtil.printTree(n1);
+        }
+    }
+}