using System;

using System.Linq;

using System.Collections.Generic;

using System.Threading.Tasks;

public class Program

{

    public static async Task Main()

    {

        var root = await GatherAsync().FirstOrDefaultAsync();

        await Task.Delay(1_000);

        Console.WriteLine(root.Children.Count);

    }

    static async IAsyncEnumerable<Node> GatherAsync()

    {

        Node root = new Node();

        yield return root;

        for(int i = 0; i < 5; i++)

        {

            var node = await GenerateNodeAsync(root);

            root.Children.Add(node);

        }

    }

    static async Task<Node> GenerateNodeAsync(Node parent)

    {

        await Task.Delay(Random.Shared.Next(1, 50));

        return new Node() { Parent = parent };

    }

}

​

public class Node

{

    public Node Parent { get; set; }

    public List<Node> Children { get; set; } = new List<Node>();

}