What is Item ID (Root ID)
Org Chart uses Item ID to find user profiles and list items and organize them properly. It is mapped according to the data source your Org Chart is pulling information from and also depending on how you mapped this information. If you open Org Chart settings again you’ll see under the “Data source settings” tab that we have two options: SharePoint list and User profiles.
In case you’re using User profiles as the data source, Org Chart will use one’s account name as the Item ID. In SharePoint Online account name will be its e-mail address but using OnPremises installation it usually looks like “domain\accountname”.
Otherwise, if you’re using a SharePoint list as the data source for your Org Chart, you’ll have the option to choose which column from the list is going to work as Item ID. It can be anything like title, e-mail address, ID, etc. Please, notice that you’ll also have to set up Item parent ID according to Item ID.