Bush is a tree branch hung as a sign before a tavern or vintner's shop.For good wine,the reputation of it is well accepted by people,so no need of such bush.It is a metaphor for that good things need not advertise themselves.
Good wine needs no bush :It means that something that is good does not need advertising. Good wine needs no bush , and perhaps products that people really want need no hard-sell or soft-sell TV push.