如何使用LINQ同时搜索所有子项

public class Item
{
    public string Name { get; set; }
    public List<Item> Children { get; set; }
}

public static IEnumerable<Item> SearchItems(IEnumerable<Item> items, string keyword)
{
    foreach (var item in items)
    {
        if (item.Name.Contains(keyword))
        {
            yield return item;
        }

        if (item.Children != null)
        {
            foreach (var child in SearchItems(item.Children, keyword))
            {
                yield return child;
            }
        }
    }
}

var rootItem = new Item
{
    Name = "Root",
    Children = new List<Item>
    {
        new Item { Name = "Item 1" },
        new Item
        {
            Name = "Item 2",
            Children = new List<Item>
            {
                new Item { Name = "Item 2.1" },
                new Item { Name = "Item 2.2" }
            }
        },
        new Item { Name = "Item 3" }
    }
};

var keyword = "Item";
var searchResults = SearchItems(new List<Item> { rootItem }, keyword);

foreach (var result in searchResults)
{
    Console.WriteLine(result.Name);
}