Afford is a synonym of Contribute. Contribute is a synonym of Help. Help is a synonym of Facilitate. 
Tree is etymologically related to True. True is related to Believe. Swallow is a type of Believe. Swallow is a type of Single. 
Afford <--Synonym--> Contribute <--Synonym--> Help <--Synonym--> Facilitate 
Tree --EtymologicallyRelatedTo--> True <--RelatedTo--> Believe <--IsA-- Swallow --IsA--> Single 