Indirect trace-function results to org-babel current-buffer

[abst.proc.do@qq.com (abst.proc.do)]

When tried to apply =trace-function= to a recursive-factorial which
print the tracing course to the current buffer:

#+BEGIN_SRC elisp
(defun factorial(n)
  (if (= n 1)
      1
      (* n (factorial (- n 1)))))
(trace-function #'factorial (current-buffer))
(factorial 4)
#+END_SRC======================================================================

1 -> (factorial 4)
| 2 -> (factorial 3)
| | 3 -> (factorial 2)
| | | 4 -> (factorial 1)
| | | 4 <- factorial: 1
| | 3 <- factorial: 2
| 2 <- factorial: 6
1 <- factorial: 24


It works as expected but report in the echo area the error :
: org-babel-insert-result: Wrong type argument: markerp, nil

Additionally, the tracing result does not append immediately to the
source code but join to its next heading.

#+BEGIN_SRC elisp
(defun factorial(n)
  (if (= n 1)
      1
      (* n (factorial (- n 1)))))
(trace-function #'factorial (current-buffer))
(factorial 4)
#+END_SRC

* Result
======================================================================
1 -> (factorial 4)
| 2 -> (factorial 3)
| | 3 -> (factorial 2)
| | | 4 -> (factorial 1)
| | | 4 <- factorial: 1
| | 3 <- factorial: 2
| 2 <- factorial: 6
1 <- factorial: 24