Display column data into rows!

Question

Hello all,

I got Oracle table with stored data as following:

Series   |    Items
_________________
A         |      1
A         |      2
A         |      3
B         |      12
B         |      5
C         |      A
C         |      D

I would like to display those data by series group in the front end application as following:

A series: 1,2,3
B series: 12,5
C series: A,D

I am not sure how to do it, so I really appreciate your time to help me. Thanks in advance.