What is the purpose of the Flutter widget tree?

The widget tree in Flutter is a hierarchical structure that represents the UI of your application.

Here's how it works:

1. Every widget in Flutter is an immutable description of part of the user interface.
2. The widget tree is built by combining multiple widgets, forming a parent-child relationship.
3. When a widget's state changes, Flutter rebuilds only the affected parts of the widget tree, improving performance.

For instance, here's a simple widget tree:

Column( children: [ Text('Hello'), Text('World') ] );

This tree consists of a Column widget containing two Text widgets.