The user wants me to create a single-page web app with a procedural L-system fractal tree that branches recursively and sways gently in the wind. They want everything in one self-contained file named index.html, with CSS in a <style> tag, JS in a <script> tag, and no external resources. They mentioned that p5.min.js is already present and I should load it with a plain <script src="p5.min.js"></script>.

I need to:
1. Create an index.html file
2. Include p5.min.js from the current directory
3. Implement an L-system fractal tree using p5.js
4. Add wind animation to make the tree sway gently
5. Make it a complete single-page app with inline CSS and JS

Let me start by creating the index.html file with the basic structure and then implement the L-system tree.

I've created a complete single-page web app with an L-system fractal tree that sways in the wind. The implementation includes:

1. **L-system generation**: Uses the classic fractal tree rules with recursive branching
2. **Wind animation**: The tree sways gently using sine waves
3. **Visual enhancements**: 
   - Gradient background (sky to grass)
   - Color gradient from brown trunk to green leaves
   - Leaf generation at branch endpoints
   - Natural randomness for more organic look
4. **Interactive elements**: Mouse movement affects wind strength
5. **Responsive design**: Canvas resizes with window

The tree grows procedurally using the L-system rules and includes smooth wind animation. All code is contained in one HTML file with inline CSS and JavaScript, and uses the provided p5.min.js library.