using System;

using System.Collections.Generic;

public class Program

{

    static void PrintNodes(List<SimpleNode> nodes)

    {

        foreach (var root in nodes)

        {

            Console.Write($"{root.Id} ");

        }

        Console.WriteLine("");

    }

    public static void Main()

    {

        /*

            A   B   C  D

            |   |   |  |

              E     |  |

              |     |  |

                 F     G

         */

​

        var tree = new SimpleTree

        {

            Nodes = new List<SimpleNode>

            {

                new SimpleNode { Id = "A" },

                new SimpleNode { Id = "B" },

                new SimpleNode { Id = "C" },

                new SimpleNode { Id = "D" },

                new SimpleNode { Id = "E" },

                new SimpleNode { Id = "F" },

                new SimpleNode { Id = "G" },

            },

            Relations = new List<SimpleNodeRelation>

            {

                new SimpleNodeRelation { ParentId = "A", ChildId = "E" },

                new SimpleNodeRelation { ParentId = "B", ChildId = "E" },

                new SimpleNodeRelation { ParentId = "C", ChildId = "F" },

                new SimpleNodeRelation { ParentId = "E", ChildId = "F" },

                new SimpleNodeRelation { ParentId = "D", ChildId = "G" },

            }

        };

    }

}

​

public class SimpleNode

{

    public string Id { get; set; } = "";

}

​

public class SimpleNodeRelation

{

    public string ChildId { get; set; } = "";

    public string ParentId { get; set; } = "";

}

​

public class SimpleTree

{

    public List<SimpleNode> Nodes { get; set; } = new();

    public List<SimpleNodeRelation> Relations { get; set; } = new();

}