As mentioned in the documentation here , it is possible to link identity by using a linking Authentication Tree. After investigation from OPENAM-16567, it is not possible to use a linking tree. Hence, it would be better to remove from documentation to avoid any confusion.
OPENAM-16602SAML Linking identities documentation indicates that a chain or tree can be used but only a chain will work
is related to
OPENAM-16567SAML module Linking Chain does not work for Authentication Tree