No trimming:
     █
  1. └─rlang:::f(0)
  2.   ├─base::identity(identity(g(n)))
  3.   ├─base::identity(g(n))
  4.   └─rlang:::g(n)
  5.     ├─base::identity(identity(h(n)))
  6.     ├─base::identity(h(n))
  7.     └─rlang:::h(n)
  8.       ├─base::identity(identity(trace_back(e, bottom = n)))
  9.       ├─base::identity(trace_back(e, bottom = n))
 10.       └─rlang::trace_back(e, bottom = n)


One layer (the default):
    █
 1. └─rlang:::f(1)
 2.   ├─base::identity(identity(g(n)))
 3.   ├─base::identity(g(n))
 4.   └─rlang:::g(n)
 5.     ├─base::identity(identity(h(n)))
 6.     ├─base::identity(h(n))
 7.     └─rlang:::h(n)


Two layers:
    █
 1. └─rlang:::f(2)
 2.   ├─base::identity(identity(g(n)))
 3.   ├─base::identity(g(n))
 4.   └─rlang:::g(n)


Three layers:
    █
 1. └─rlang:::f(3)
