When assigning an object to another object of the same type, it means that the stack information of the two objects is the same. When you want to change a property of an object and add it to a list, it will be replaced by the last object, and you cannot add a new object. The following two methods can realize the assignment of objects to objects of the same type. The stack information of these two objects is different.

Method 1:

Object must be serialized

   public static object DeepClone(object obj)
    {
        BinaryFormatter bFormatter = new BinaryFormatter();
        MemoryStream stream = new MemoryStream();
        bFormatter.Serialize(stream, obj);
        stream.Seek(0, SeekOrigin.Begin);
        return bFormatter.Deserialize(stream);
    }

Test:

[Serializable]
class User
{
    public User(){}
    public int id;
    public string name;
    public User(int id, string name)
    {
        this.id = id;
        this.name = name;
    }
}

public class test : MonoBehaviour {
    List<User> users;
    User user;
    // Use this for initialization
    void Start () {
        users = new List<User>();
        user = new User(2,"Floret");
    }
    int b = 5;
    private void Update()
    {
        if (Input.GetKeyDown(KeyCode.Q))
        {
            var a = new User();
            a = GameTool.DeepClone(user) as User;
            a.id = b++;
            users.Add(a);
        }
    }
}

Method two:

 public static object CopyObject(object obj)
    {
        object targetDeepCopyObj;

        if (obj == null)
        {
            Debug.Log("copy obj is null");
        }
        var targetType = obj.GetType();
        //Value type  
        if (targetType.IsValueType == true)
        {
            targetDeepCopyObj = obj;
        }
        //reference type   
        else
        {
            targetDeepCopyObj = Activator.CreateInstance(targetType);   //Create reference object   
            MemberInfo[] memberCollection = obj.GetType().GetMembers();

            foreach (MemberInfo member in memberCollection)
            {
                if (member.MemberType == MemberTypes.Field)
                {
                    FieldInfo field = (FieldInfo)member;
                    object fieldValue = field.GetValue(obj);
                    if (fieldValue is ICloneable)
                    {
                        field.SetValue(targetDeepCopyObj, (fieldValue as ICloneable).Clone());
                    }
                    else
                    {
                        field.SetValue(targetDeepCopyObj, CopyObject(fieldValue));
                    }

                }
                else if (member.MemberType == MemberTypes.Property)
                {
                    PropertyInfo myProperty = (PropertyInfo)member;
                    MethodInfo info = myProperty.GetSetMethod(false);
                    if (info != null)
                    {
                        object propertyValue = myProperty.GetValue(obj, null);
                        if (propertyValue is ICloneable)
                        {
                            myProperty.SetValue(targetDeepCopyObj, (propertyValue as ICloneable).Clone(), null);
                        }
                        else
                        {
                            myProperty.SetValue(targetDeepCopyObj, CopyObject(propertyValue), null);
                        }
                    }
                }
            }
        }
        return targetDeepCopyObj;
    }
    public static void CopyObject(object source, object target)
    {
        var targetType = target.GetType();
        if (targetType == null)
        {
            targetType = source.GetType();
        }
        //Value type  
        if (targetType.IsValueType == true)
        {
            target = source;
        }
        //reference type   
        else
        {
            if (source == null)
            {
                return;
            }
            MemberInfo[] memberCollection = source.GetType().GetMembers();

            foreach (MemberInfo member in memberCollection)
            {
                if (member.MemberType == MemberTypes.Field)
                {
                    FieldInfo field = (FieldInfo)member;
                    object fieldValue = field.GetValue(source);
                    if (fieldValue is ICloneable)
                    {
                        field.SetValue(target, (fieldValue as ICloneable).Clone());
                    }
                    else
                    {
                        field.SetValue(target, CopyObject(fieldValue));
                    }

                }
                else if (member.MemberType == MemberTypes.Property)
                {
                    PropertyInfo myProperty = (PropertyInfo)member;
                    MethodInfo info = myProperty.GetSetMethod(false);
                    if (info != null)
                    {
                        object propertyValue = myProperty.GetValue(source, null);
                        if (propertyValue is ICloneable)
                        {
                            myProperty.SetValue(target, (propertyValue as ICloneable).Clone(), null);
                        }
                        else
                        {
                            myProperty.SetValue(target, CopyObject(propertyValue), null);
                        }
                    }

                }
            }
        }
    }

Test:

class User
{
    public User(){}
    public int id;
    public string name;
    public User(int id, string name)
    {
        this.id = id;
        this.name = name;
    }
}

public class test : MonoBehaviour {
    List<User> users;
    User user;
    // Use this for initialization
    void Start () {
        users = new List<User>();
        user = new User(2,"Floret");
    }
    int b = 5;
    private void Update()
    {
        if (Input.GetKeyDown(KeyCode.Q))
        {
            var a = new User();
            a = GameTool.CopyObject(user) as User;
            a.id = b++;
            users.Add(a);
        }
    }
}

Test result keyu can view users data at breakpoint