try another way to implement the data stucture

UserService.Infrastructure/DataModels/Member.cs

@@ -4,8 +4,6 @@ namespace UserService.Infrastructure.DataModels
 {
     public abstract class Member : Node
     {
-        public ISet<MembersMember> Members { get; set; } = new HashSet<MembersMember>();
-
         public ISet<MembersMember> MemberOf { get; set; } = null!;
     }
 }

UserService.Infrastructure/DataModels/Node.cs

@@ -5,29 +5,15 @@ using System.ComponentModel.DataAnnotations;
 
 namespace UserService.Infrastructure.DataModels
 {
-    public abstract class Node : ICloneable, IComparable<Node>
+    public abstract class Node : ICloneable
     {
-        public Guid Id { get; set; }
+        public int Id { get; set; }
         [Required] public string CommonName { get; set; } = null!;
         public string? Description { get; set; }
-        public ISet<Node> Children { get; set; } = new SortedSet<Node>();
-        public Node? Parent { get; set; } //Parent
-        public Guid? ParentId { get; set; }
-
         public override string ToString() => CommonName;
-
-        public int Level => Parent?.Level + 1 ?? 0;
+        public int? ParentId { get; set; }
 
         /// <inheritdoc />
         public virtual object Clone() => MemberwiseClone();
-
-        public int CompareTo(Node? other)
-        {
-            if (ReferenceEquals(this, other)) return 0;
-            if (other is null) return 1;
-            var commonNameComparison = string.Compare(CommonName, other.CommonName, StringComparison.Ordinal);
-            if (commonNameComparison != 0) return commonNameComparison;
-            return Id.CompareTo(other.Id);
-        }
     }
 }

UserService.Infrastructure/DataModels/OrganizationUnit.cs

@@ -1,4 +1,6 @@
-namespace UserService.Infrastructure.DataModels
+using System.Collections.Generic;
+
+namespace UserService.Infrastructure.DataModels
 {
     public class OrganizationUnit : Node
     {

UserService.Infrastructure/DataModels/SecurityGroup.cs

@@ -1,6 +1,9 @@
-namespace UserService.Infrastructure.DataModels
+using System.Collections.Generic;
+
+namespace UserService.Infrastructure.DataModels
 {
     public class SecurityGroup : Member
     {
+        public ISet<MembersMember> Members { get; set; } = new HashSet<MembersMember>();
     }
 }