error[E0502]: cannot borrow `*root` as mutable because it is also borrowed as immutable
  --> tests/compile_fail/use_root_mutably_while_bound.rs:11:5
   |
10 |     let v = root.add(0);
   |             ----------- immutable borrow occurs here
11 |     use_root(&owner, root, v);
   |     --------^^^^^^^^^^^^^^^^^
   |     |
   |     mutable borrow occurs here
   |     immutable borrow later used by call