Apex Developer Guide
jNote: This release is in preview. Features described here don’t become generally available until the latest general availability date that Salesforce announces for this release. Before then, and where features are noted as beta, pilot, or developer preview, we can’t guarantee general availability within any particular time frame or at all. Make your purchase decisions only on the basis of generally available products and features.
Triggers and Recovered Records
The after undelete trigger event only works with recovered records—that is, records that were deleted and then recovered from the Recycle Bin through the undelete DML statement. These are also called undeleted records.
The after undelete trigger events only run on top-level objects. For example, if you delete an Account, an Opportunity may also be deleted. When you recover the Account from the Recycle Bin, the Opportunity is also recovered. If there is an after undelete trigger event associated with both the Account and the Opportunity, only the Account after undelete trigger event executes.