Now there is an extra function BKE_libblock_free_data, which is called explicitly in ntreeFreeTree if the tree is not part of the library data (ntreeCopyTree does a similar thing using BKE_libblock_copy_data).
Now there is an extra function BKE_libblock_free_data, which is called explicitly in ntreeFreeTree if the tree is not part of the library data (ntreeCopyTree does a similar thing using BKE_libblock_copy_data).