Air carrier First Officer reported there are two taxiways marked with the same designation at WSSS and the reporter's confirmation bias led the flight crew to make the wrong turn.

Narrative

Landed Runway 20R and was told by Tower to turn left on W7 and left on W and to contact Ground. Exiting Runway 20R there are two taxiways with W7 designation. We exited and the CA was making the turn on W7 to the left. I saw the taxi sign with W7 to the right and said we needed to turn right on W7 and then left on W. I didn't see the other taxiway sign with W7 on it. We exited the runway and Ground instructed us to turn right on W now and informed us we made a wrong turn. There were no traffic conflicts and we taxied around the south terminal to our gate.Cause: Having two taxiways with the same designation. And confirmation bias of myself with the taxi sign saying W7 to the right. I've been to WSSS many times and I've never noticed this before.Suggestions: Have a plan on runway exit and be more aware that some taxi exits that turn different directions share the same identifier. I will be more throughout in my studying the taxi chart in the future to ensure this type of mistake doesn't happen again.