getter functions for custom objects

# New Feature

- What's your use case? I'm working on a company app that requires this package, I have the data to display already converted to a tree structure, but I can't change the variable names of the treeData because I'm using another similar package for other things.
- What interface do you have in mind? New methods: getTitle, getChildren, getId, getParentId, etc. Just getter methods to use custom objects.

Example:

`
nodes }
getParentId={ ({ parentId }) => parentId }
...
/>
`