trace a nested recursion in Ocaml

I am trying to understand deeply nested recursion in OCaml by using the sorting list algorithm. For this reason I am tracing the below code which has a recursive function sort and calls another function insert.

let rec sort (lst : int list) =  match lst with [] -> [] | head :: tail -> insert head (sort tail)and insert elt lst =  match lst with  | [] -> [ elt ]  | head :: tail -> if elt <= head then elt :: lst else head :: insert elt tail

I understand the first recursive calls for sort, but after that I cannot follow.

For instance, suppose we have the list [6, 2, 5, 3]. After sorting the tail of this list as 2,3,5 where in the code the head6 is compared to each element of this tail? Can somebody provide a hint for the trace results?

utop # sort [6; 2; 5; 3];;        > sort <-- [6; 2; 5; 3]                                                 > sort <-- [2; 5; 3]                                                    > sort <-- [5; 3]                                                       > sort <-- [3]                                                          > sort <-- []                                                           > sort --> []                                                           > insert <-- 3                                                          > insert -->                                                            > insert* <-- []                                                        > insert* --> [3]                                                       > sort --> [3]                                                          > insert <-- 5                                                          > insert -->                                                            > insert* <-- [3]                                                       > insert <-- 5                                                          > insert -->                                                            > insert* <-- []                                                        > insert* --> [5]                                                       > insert* --> [3; 5]                                                    > sort --> [3; 5]                                                       > insert <-- 2                                                          > insert -->                                                            > insert* <-- [3; 5]                                                    > insert* --> [2; 3; 5]                                                 > sort --> [2; 3; 5]                                                    > insert <-- 6                                                          > insert -->                                                            > insert* <-- [2; 3; 5]                                                 > insert <-- 6                                                          > insert -->                                                            > insert* <-- [3; 5]                                                    > insert <-- 6                                                          > insert -->                                                            > insert* <-- [5]                                                       > insert <-- 6                                                          > insert -->                                                            > insert* <-- []                                                        > insert* --> [6]                                                       > insert* --> [5; 6]                                                    > insert* --> [3; 5; 6]                                                 > insert* --> [2; 3; 5; 6]                                              > sort --> [2; 3; 5; 6]                                                 > > - : int list = [2; 3; 5; 6]**