Could you help identify this small tree in my back yard?
Hello. This is a type of Mahonia. They are planted as ornamental shrubs, but two species, Mahonia bealei and Mahonia repens, have been found to have invasive tendencies in our area and may show up as "volunteers" by way of seed dispersal. If you decide to keep it, I recommend trimming off the flowers/fruits to avoid spread of the seeds into natural areas.
Here is our information about invasive plants,