API name of Entitlement Process is SlaProcess. API name of Milestones is MilestoneType. API name of Milestones applied to cases is CaseMilestone.
An Entitlement Process consists of milestones. But MilestoneType is merely the template for the milestones added to an Entitlement Process; when you add a Milestone to an EP, you specify additional attributes such as Minutes to Complete Milestone.
Adding milestones to EPs through the UI is time-consuming so I'd like to be able to mass create milestones-in-entitlement-processes. But it's not clear what that object is called or whether it's exposed through the API. Oddly, SlaProcess and related objects are absent from the ERD
What object is a milestone added to an entitlement process, and can it be written from the API?