ImportError: You must install graphviz to plot tree

To resolve the `ImportError` and be able to plot the tree, you need to install the Graphviz library. Here's how you can do it:

1. If you haven't installed Graphviz yet, you can do so using a package manager like pip or conda.

Using pip:

   pip install graphviz

Using conda:

   conda install graphviz

2. Once Graphviz is installed, you might also need to install the Graphviz system package on your machine. Refer to the Graphviz documentation for instructions on how to install it based on your operating system.

Graphviz website: https://graphviz.org/

3. After installing both the Python library and the system package, you should be able to import and use Graphviz to plot the tree without encountering the `ImportError` anymore.

If you still face any issues, please provide more details about the specific code or context where you're experiencing this error, and I'll be glad to assist you further.