如何在linq中将树展平为表

using System;
using System.Collections.Generic;
using System.Linq;

public class TreeNode
{
    public int Id { get; set; }
    public string Name { get; set; }
    public List<TreeNode> Children { get; set; }
}

public static class TreeExtensions
{
    public static IEnumerable<TreeNode> Flatten(this TreeNode root)
    {
        yield return root;

        if (root.Children != null)
        {
            foreach (var child in root.Children)
            {
                foreach (var flattenedChild in child.Flatten())
                {
                    yield return flattenedChild;
                }
            }
        }
    }
}

public class Program
{
    public static void Main()
    {
        // 构建一个树结构
        var root = new TreeNode
        {
            Id = 1,
            Name = "Root",
            Children = new List<TreeNode>
            {
                new TreeNode
                {
                    Id = 2,
                    Name = "Child 1",
                    Children = new List<TreeNode>
                    {
                        new TreeNode { Id = 4, Name = "Grandchild 1" },
                        new TreeNode { Id = 5, Name = "Grandchild 2" }
                    }
                },
                new TreeNode
                {
                    Id = 3,
                    Name = "Child 2",
                    Children = new List<TreeNode>
                    {
                        new TreeNode { Id = 6, Name = "Grandchild 3" }
                    }
                }
            }
        };

        // 使用Flatten方法将树展平为表
        var flattenedTree = root.Flatten();

        // 打印展平后的结果
        foreach (var node in flattenedTree)
        {
            Console.WriteLine($"Id: {node.Id}, Name: {node.Name}");
        }
    }
}