Remove list element

AddTabGroupChildren(Config.KpiSelection.TabHierarchy.TabBase);
private void AddTabGroupChildren(List<XmlTabBase> members)
{
    members = members
        .OrderBy(p => p.Order)
        .ToList();

    var children = members.OfType<XmlTabGroup>().ToLookup(group => group.GroupId);
    foreach (var member in members.OfType<XmlTabGroup>().ToList())
    {
        member.TabBase.AddRange(new List<XmlTabGroup>(children[member.Order].ToList()));
        member.TabBase = member.TabBase.OrderBy(p => p.Order).ToList();
        if (member.GroupId != 0) members.RemoveAt(members.FindIndex(p => p.Order == member.Order));
    }
}

AddTabGroupChildren(Config.KpiSelection.TabHierarchy.TabBase);
private void AddTabGroupChildren(List<XmlTabBase> members)
{
    members = members
        .OrderBy(p => p.Order)
        .ToList();

    var children = members.OfType<XmlTabGroup>().ToLookup(group => group.GroupId);
    foreach (var member in members.OfType<XmlTabGroup>().ToList())
    {
        member.TabBase.AddRange(new List<XmlTabGroup>(children[member.Order].ToList()));
        member.TabBase = member.TabBase.OrderBy(p => p.Order).ToList();
        if (member.GroupId != 0) members.RemoveAt(members.FindIndex(p => p.Order == member.Order));
    }
}