INDEX & MATCH multiple rows to return comma separated cell

Trying to create a comma separated cell with values from column A by matching a string in column B:

A B
Item1 X
Item2 Y
Item3 Z
Item4 Z
Item5 Y
Item6 Z

Say I want to get all the items in column A that has a "Z" in column B. How can I make a formula that would return:

Item3, Item4, Item6

Here's what I tried, but can only return the 1st item (Item3):

=INDEX(A1:A6,MATCH("Z",B1:B6,0))