Tree-double pointer

I have one question about double pointers . For exemple inserting node in tree

Code:

int insert( cvor [B]**glava[/B] , char *name , float number ) {

        cvor *temp;
        int where ; 

        if ( *glava == NULL ) {
        temp = (cvor*)malloc(sizeof(cvor) ) ;
        if (temp == NULL ) printf("error");
        temp->left = temp->right = NULL ; 
        strcpy ( temp->name, name ) ;
        temp->number = number;
        *glava = temp ;
        return 1;
        } else { 
                where = strcmp (name , (*glava)->name);
                if ( !where ) return -1;
                if ( where < 0 ) return dodaj( &((*glava)->left) , name , number ) ; 
                return dodaj( &((*glava)->right) , name , number ) ; 
        }

} 

So why must be double pointer in this function (Bold) ? Or in creating list ?