How to stretch the image on the button?

[Mikeeeeee]

Hi.
How to stretch the image on the button?
I put the picture like this, but the picture does not stretch.

ui->buttonR->setStyleSheet("background-image: url(:/Images/Images/flagRus.png);");

[Mikeeeeee]

ui->buttonRus->setStyleSheet("border-image: url(:/Images/Images/flagRus.png) stretch; ");