Eurasian Tree Sparrows (Passer montanus) look similar to House Sparrows (Passer domesticus).
If you want to tell them apart, remember that Eurasian Tree Sparrows have a brown cap and House Sparrows have a grey cap.
Male and female House Sparrows look different while male and female Eurasian Tree Sparrows look similar.
The Eurasian Tree Sparrow is the usual sparrow one sees in Singapore.
The House Sparrow is rare in Singapore and it seems that nowadays it can only be found at Jurong Island.

Pulau Ubin, Singapore, 24 October 2022