How to set background color of each node in react-sortable-tree package

# Reporting a Bug?

Please include either a failing unit test or a simple reproduction. You can start by forking the [CodeSandbox example](https://codesandbox.io/s/wkxvy3z15w)

# Requesting a Feature?

Provide as much information as possible about your requested feature. Here are a few questions you may consider answering:
* What's your use case? (Tell me about your application and what problem you're trying to solve.)
* What interface do you have in mind? (What new properties or methods do you think might be helpful?)
* Can you point to similar functionality with any existing libraries or components? (Working demos can be helpful.)