What is idiomatic way in f# to express sequence of if statements with overlapping conditions

Let's say I got code like this:

if(conditionA)
    do something
if(conditionA && conditionB)
    do something more

Obviously, I could nest the ifs (although when there are more complicated conditions this is not readable for me) like below:

if(conditionA)
    do something
    if(conditionB)
        do something more

How can I write similar code in f# idiomatically. I assume if statement isn't considered idiomatic in functional programming (am I wrong?)

I could write two subsequent match expressions or nested match expression to mimic above code but doing so seems pretty ugly to me.