public static HierarchyId GeneratePathForChild(HierarchyId? parent, HierarchyId? lastChildId)
{

    //Handling Fatherless Entities.
    if (parent is null)
        return HierarchyId.Parse("/");

    //Handling Entities With No Sister Entities.
    if (lastChildId is null)
        return HierarchyId.Parse($"{parent}{1}/");

    //Handling Entities With Sister Entities
    var lastDigit = lastChildId.ToString().Split("/", StringSplitOptions.RemoveEmptyEntries).Last();
    var lastDigitNumber = int.Parse(lastDigit);
    return HierarchyId.Parse($"{parent}{lastDigitNumber + 1}/");

}

public static HierarchyId GeneratePathForChild(HierarchyId? parent, HierarchyId? lastChildId)
{

    //Handling Fatherless Entities.
    if (parent is null)
        return HierarchyId.Parse("/");

    //Handling Entities With No Sister Entities.
    if (lastChildId is null)
        return HierarchyId.Parse($"{parent}{1}/");

    //Handling Entities With Sister Entities
    var lastDigit = lastChildId.ToString().Split("/", StringSplitOptions.RemoveEmptyEntries).Last();
    var lastDigitNumber = int.Parse(lastDigit);
    return HierarchyId.Parse($"{parent}{lastDigitNumber + 1}/");

}