I've a plant growing in my garden, that I'm hoping somebody can identify. I live in zone 5b or 6a, on the Plant Hardiness Zone Map. 

It's about 2-3' tall, has dark red leaves,

![Red leaf](https://i.stack.imgur.com/oeT62.jpg)
![Leaf size](https://i.stack.imgur.com/9iJtC.jpg)

gets little white flowers in the spring,

![White flower](https://i.stack.imgur.com/L7Kzk.jpg)
![Flower closeup](https://i.stack.imgur.com/wXw7t.jpg)

and has a dark colored bark.

![Dark bark](https://i.stack.imgur.com/EaOoi.jpg)

What is this plant?