When printing a tree, the root node is preceded with R——

The following code:
```python
bst = RedBlackTree()
bst.insert(1)
bst.insert(2)
bst.insert(3)
bst.print_tree()
```

produces the following output:
```
R----  2(BLACK)
     L----   1(RED)
     R----  3(RED)
```
I feel the following would be more appropriate:

```
2(BLACK)
     L----  1(RED)
     R----  3(RED)
```

let me know if you disagree:

