1 AddMul(variant = "ADD",)
2 ├─ AddMul(variant = "MUL",)
3 │  ├─ Const(2)
4 │  └─ Sym(x)
5 └─ Sym(z)

Hint: call SymbolicUtils.pluck(expr, line_number) to get the subexpression starting at line_number