如果父id相同，则合并子项的Linq查询

// 假设我们有一个包含子项的列表
List<Item> items = new List<Item>
{
    new Item { Id = 1, ParentId = 1, Name = "Item 1" },
    new Item { Id = 2, ParentId = 1, Name = "Item 2" },
    new Item { Id = 3, ParentId = 2, Name = "Item 3" },
    new Item { Id = 4, ParentId = 2, Name = "Item 4" },
    new Item { Id = 5, ParentId = 3, Name = "Item 5" },
    new Item { Id = 6, ParentId = 3, Name = "Item 6" }
};

// 使用Linq查询合并具有相同父id的子项
var mergedItems = items.GroupBy(i => i.ParentId)
                       .SelectMany(g => g);

// 输出合并后的子项
foreach (var item in mergedItems)
{
    Console.WriteLine($"Id: {item.Id}, ParentId: {item.ParentId}, Name: {item.Name}");
}