Do you happen to know what kind of tree I am growing? The berries are quite purple and look like a skirt on the tree.
Mahonia are fairly common around here. Perhaps you have heard the common name Oregon grape. Wild species of Mahonia are easy to find in the wild here as well. Research shows that the genus falls with Berberis, so it will be found listed under both names depending on the taxonomic view of the publisher. The berries are edible and very high in vitamin C. The flavour is very sour and intense though, so best made into preserves or added to sweet fruit.
Most independent garden centers here stock examples of the cross such as 'Arthur Menzies', 'Charity', 'Lionel Fortescue' and 'Winter Sun'.