用id递归遍历树，同时添加到列表中

我怎么能递归地遍历我的树与Id，终止当它击中根而添加到List<User> ?我尝试过ref和out的不同组合，没有运气。

我试图修改dotnetpearls示例:

static int Recursive(int value, ref int count)
{
    count++;
    if (value >= 10)
    {
        // throw new Exception("End");
        return value;
    }
    return Recursive(value + 1, ref count);
}
static void Main()
{
    //
    // Call recursive method with two parameters.
    //
    int count = 0;
    int total = Recursive(5, ref count);
    //
    // Write the result from the method calls and also the call count.
    //
    Console.WriteLine(total);
    Console.WriteLine(count);
}

到像这样的东西:

static void Main(string[] args)
{
    List<int> userIds = new List<int>();
    Recursive(5, ref userIds);
    Console.WriteLine(userIds);
    Console.ReadKey();
}
static int Recursive(int nodeId, ref List<int> userIds)
{
    userIds.AddRange(GetPersonIdsOnThisNode(nodeId)); // Error: Argument type 'int' is not assignable to parameter type 'System.Collections.Generic.IEnumerable<int>'
    if (nodeId >= 10)
    {
        return nodeId; // I don't care about the return value. I only care about populating my list of userId's.
    }
    return Recursive(nodeId + 1, ref userIds);
}
static int GetUserIdsOnThisNode(int nodeId)
{
    return 3;
}