We have extended our little birch copse with two Himalayan White Birch trees Betula utitis var. jacquemontii. They are quite mature standards so it remains to be seen whether they will take an thrive. We have done all the right things: lots of Rootgrow; a big hole, back-filled with compost rich soil mixture, lots of water.
As a counterpoint to the white-barked birch we put in a black-barked flowering cherry (well ornamental plum) Prunus cerasifera var. Pissardii Nigra