using System;

public class Program

{

    public static void Main()

    {

        var t1 = new TreeItem() {Value = 1};        

        var t2 = new TreeItem() {Value = 10};

        var t5 = new TreeItem() {Value = 9};

        var t3 = new TreeItem() {Value = 30};

        t2.Left = t5;

        t5.Left = t1;       

        t2.Right = t3;      

        t2.PrintPretty(string.Empty, true, false);

        Console.WriteLine();

        var t4 = new TreeItem() {Value = 7};

        InsertNode(t2, t4);

        var t6 = new TreeItem() {Value = 20};

        InsertNode(t2, t6);

        t2.PrintPretty(string.Empty, true, false);

    }

    private static void InsertNode(TreeItem tree, TreeItem item) {

        var currentNode = tree;

        while (true) {

            if (item.Value >= currentNode.Value) {

                if (currentNode.Right == null) {

                    currentNode.Right = item;

                    break;

                }

                else 

                    currentNode = currentNode.Right;

            }

            else {

                if (currentNode.Left == null) {

                    currentNode.Left = item;

                    break;

                }

                else {

                    currentNode = currentNode.Left;

                }

            }

        }

    }

}

​

public class TreeItem {

    public int Value {get;set;}

    public TreeItem Left {get;set;}

    public TreeItem Right {get;set;}

    public void PrintPretty(string indent, bool left, bool hasRight)

    {

        Console.Write(indent);

        if (left)

        {

            Console.Write("l-");

        }

        else

        {

            Console.Write("r-");

        }

        if (left && hasRight) {

            indent += "|  ";

        }

        else {

            indent += "   ";

        }

        Console.WriteLine(Value);

        Left?.PrintPretty(indent, true, Right != null);

        Right?.PrintPretty(indent, false, false);

    }

}