You can disable Notifications which will prevent the new item being loaded like so:
Client.Site.Notifications.Disabled = true;
TemplateItem template = db.GetTemplate(TemplatePath);
Item parentItem = db.Items[ItemsRootPath];
var newItem = parentItem.Add("item name", template);
Client.Site.Notifications.Disabled = false;
I tested this by adding a child to the item that I was saving and resulted in the tree not being updated as well. I fixed that by adding this line after the notification enable.
Sitecore.Context.ClientPage.SendMessage(this, string.Format("item:refreshchildren(id={0})", ItemID));