There is no way to choose a tree-based implementation of social login within the "Social Authentication Implementations". The UI only allows you to choose from whatever social chains are defined.
If the service is configured using amster/rest, the name of the tree can be provided and the service will work as expected from the XUI login page.
1) Start the embedded DJ configuration with the example auth trees
2) Create a new instance of the "Social Authentication Implementations" service
3) Try to specify the "Facebook-ProvisionIDMAccount" as a value under "Authentication Chains"
You can choose the tree and it works the same as the equivalent chain.
The UI does not present the tree as an option. Any attempt to manually type the tree name is discarded upon saving.
Use amster/rest to specify the value instead of the UI.