Resolve ambiguous access reported by msvc

calligra\sheets\RTree.h(315): error C2385: ambiguous access of 'Node'
calligra\sheets\RTree.h(315): note: could be the 'Node' in base 'Calligra::Sheets::RTree<`template-type-parameter-1'>'
calligra\sheets\RTree.h(315): note: or could be the 'Node' in base 'KoRTree<`template-type-parameter-1'>'
calligra\sheets\RTree.h(341): note: see reference to class template instantiation 'Calligra::Sheets::RTree<T>::LeafNode' being compiled
calligra\sheets\RTree.h(350): error C2385: ambiguous access of 'Node'
calligra\sheets\RTree.h(350): note: could be the 'Node' in base 'Calligra::Sheets::RTree<`template-type-parameter-1'>'
calligra\sheets\RTree.h(350): note: or could be the 'Node' in base 'KoRTree<`template-type-parameter-1'>'
calligra\sheets\RTree.h(373): note: see reference to class template instantiation 'Calligra::Sheets::RTree<T>::NonLeafNode' being compiled