how to make unequalled axis interval

I have a large number of data ranging from 0 to 20. However, most of these data are clustered between 0 to 5, which means the data ranging from 6 to 20 are sparse. If plotting out as plot(data), I can see a big cluster around y-range [0 5]. Is it possible to increase the y-axis interval between 0 and 5, so the data distribution will become clear. But, I do want to make the y-axis interval for the range [6, 20] smaller, so the data there will become denser.