It wouldn't be important with such a small number of conditional branches, but the basic idea, trying to put it plainly, is that it would reduce the possibility of a lot of conditional branches being gone through by eliminating by halves. Take for instance, if you had eight possibilities. Then one way to do it would be:
if var == 1
else
if var == 2
else
if var == 3
else
...
if var == 8
end
...
end
So, in the case where the value of the variable is 8, then that would have to check the conditions eight times every time it goes through. The purpose of a binary tree would be to reduce the maximum number of conditionals, though this may also raise the minimum number of conditionals.
So, you could rewrite that and have it as this instead:
if var <= 4
if var <= 2
if var == 1
# code for when var == 1
else
# code for when var == 2
end
else
if var == 3
# code for when var == 3
else
# code for when var == 4
end
end
else
if var <= 6
if var == 5
# code for when var == 5
else
# code for when var == 6
end
else
if var == 7
# code for when var == 7
else
# code for when var == 8
end
end
end
That way, there would only be three checks necessary, no matter what the variable is. So it reduces the worst case scenario. It would become particularly important where there are lots and lots of options, like for instance, 128 possibilities.