IfcDoc.CtlRules.MoveRule C# (CSharp) Method

        private void MoveRule(int offset)
        {
            TreeNode tnSelect = this.treeViewTemplate.SelectedNode;
            TreeNode tnParent = tnSelect.Parent;
            DocModelRule ruleSelect = (DocModelRule)tnSelect.Tag;
            if (tnParent.Tag is DocModelRule)
            {
                DocModelRule ruleParent = (DocModelRule)tnParent.Tag;
                int index = ruleParent.Rules.IndexOf(ruleSelect);
                ruleParent.Rules.RemoveAt(index);

                index += offset;

                ruleParent.Rules.Insert(index, ruleSelect);
                tnSelect.Remove();
                tnParent.Nodes.Insert(index, tnSelect);
            }
            else if (tnParent.Tag is DocTemplateDefinition)
            {
                DocTemplateDefinition ruleParent = (DocTemplateDefinition)tnParent.Tag;
                int index = ruleParent.Rules.IndexOf(ruleSelect);
                ruleParent.Rules.RemoveAt(index);

                index += offset;

                ruleParent.Rules.Insert(index, ruleSelect);
                tnSelect.Remove();
                tnParent.Nodes.Insert(index, tnSelect);
            }

            this.treeViewTemplate.SelectedNode = tnSelect;
        }