[SiNTAX]

I don't know anything about slowaris, but you could look in the glibc sources (but don't forget, this is GPL code)
ie.. glibc-2.3.2/misc/tsearch.c :

/* The standardized functions miss an important functionality: the
tree cannot be removed easily.  We provide a function to do this.  */
static void
internal_function
tdestroy_recurse (node root, __free_fn_t freefct)
{
if (root->left != NULL)
tdestroy_recurse (root->left, freefct);
if (root->right != NULL)
tdestroy_recurse (root->right, freefct);
(*freefct) ((void *) root->key);
/* Free the node itself.  */
free (root);
}
void
__tdestroy (void *vroot, __free_fn_t freefct)
{
node root = (node) vroot;
CHECK_TREE (root);
if (root != NULL)
tdestroy_recurse (root, freefct);
}
weak_alias (__tdestroy, tdestroy)