printf("Pointer to tree is %p\n", (void*) tree);
doc = caml_alloc_custom(&ops,sizeof(XMLTree*),1,2);
memcpy(Data_custom_val(doc),&tree,sizeof(XMLTree*));
printf("Pointer to tree is %p\n", (void*) tree);
doc = caml_alloc_custom(&ops,sizeof(XMLTree*),1,2);
memcpy(Data_custom_val(doc),&tree,sizeof(XMLTree*));