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?