The following snippet was taken from https://nim-lang.org/docs/tut2.html#generics

if c < 0:
  if it.le == nil:
      it.le = n
      return
  it = it.le
else:
  if it.ri == nil:
    it.ri = n
    return
  it = it.ri

As you can see the if and the else block have identical logic, with the only difference being
that they operate on different variables.

Actually this sort of code where you refactor it by creating a intermediary reference
for the thing you want to do something to, is rather common in programming, which is
why a different notation might be nice:

if c < 0: it.le else: it.ri
  if context == nil:
    context = n
    return
  it = context

Here the if-else is one-lined and two distinguishing factor is automatically
referenced by the compiler generated context identifier. Once the programmer knows how
this works, this should be pretty easy to write/read/maintain.