cant understand the last part of this merging proccess

Code:

---

typedef struct node node;
struct node{
        int value,count;
        node *lc,*rc;
};

node * CopyOf (node* T)
{
        if (T ==NULL)
                return  NULL;
        node* temp;
        temp = (node *)malloc(sizeof(node));

        temp-> value = T->value;
        temp->lc  =  CopyOf(T->lc);
        temp->rc =  CopyOf(T->rc);
        return  temp;
}

node * Merge(node* T1 , node* T2)
{
  node* result, *temp, *aux;

  if ((!T1)&&(!T2))
          return  NULL;
  if (!T1)
          return  T2;
  if (!T2)
          return  T1;
       
  temp =(node *)malloc(sizeof(node));
  temp-> value = T1->value;
  temp->lc  = temp->rc = NULL;

  aux = Merge(T2, T1->lc);
  result = Merge(aux, T1->rc);
  BST_insert( temp,  &result);
  return result;
}

---

the main function is merge
it takes two bst trees and merge them into one big copy new bst tree.
insert is a helping function which adds a new node to the tree

i cant understand the merging last past
how they use aux
whats the schematics of this?