Each item in the tree can only be edited by one user at a time.
If an item is viewed by several users, each viewer can see other the users avatar next to the item id:
If another user is editing an item, it is indicated, by a red hue and the item become readonly for the other users
If the other users saves the changes, the item will be automatically updated for the viewers.
While concurrent edit is normally prevented by the UI, it can happen when using the API or after timeouts (e.g. if someone forgets to save in the evening). In this case a dialog will instruct the user how to merge the changes.