What is the name of the bias that associate a thing as good because it has a relation to another good thing? A customer buys X from "brand A" and has positive experience with it. "Brand A" also sells Y. Now the customer things it is good to buy Y because of his/her positive experience with buying X from brand A and that since it was good, buying Y from brand A should also be good. They bought Y because of association. 

What would be the name of the psychological process or cognitive bias that lead the customer to buy Y ?
It's called the Halo Effect:


  The halo effect is a ... cognitive bias, where a person making an
  initial assessment of another person, place, or thing will assume
  ambiguous information based upon concrete information.
  
  The term halo effect is used in marketing to explain customer bias
  toward certain products because of favorable experience with other
  products made by the same company. ... A notable example is the manner
  in which the popularity of Apple’s iPod generated enthusiasm for the
  corporation's other products.