Place inside your Unity projects Asset folder, as such: Assets -> Scripts -> Editor. Allows you to easily mark assets to be bundled

AssetBundler.cs

using UnityEngine;
using UnityEditor;
using System.IO;

public class AssetBundler : Editor {

    [MenuItem("Assets/Build AssetBundles")]
    static void BuildAllAssetBundles() {
        string exportPath = ASSET_BUNDLE_OUTPUT_PATH; // Change to fit your needs
        BuildPipeline.BuildAssetBundles(exportPath, BuildAssetBundleOptions.ChunkBasedCompression, BuildTarget.StandaloneWindows64); // Change Options to fit your needs
    }
    
    private static AssetImporter assetImporter;
    private static string ASSETS_TO_BUNDLE_PATH = Application.dataPath + @"\Resources\ResourcesToPutInBundle";
    private static string ASSET_BUNDLE_OUTPUT_PATH = Application.dataPath + @"\Resources\AssetBundles";
    private static string ASSET_BUNDLE_VARIANT = "";

    // Comment out method when not being used //
    [MenuItem("Assets/Mark Assets To Be Bundled")]
    static void MarkAssetsToBeBundled () {
        // This method assumes that you have created a directory to store all assets that you want to be marked for a bundled.
        // This method then iterates through all subdirectories and marks every prefab in those subdirectories that you wish to be bundled.
        DirectoryInfo rootDirectory = new DirectoryInfo(ASSETS_TO_BUNDLE_PATH); // Get root directory
        DirectoryInfo[] subDirectories = rootDirectory.GetDirectories(); // Get all subdirectories
 
        foreach(DirectoryInfo assetDirectory in subDirectories) { // Iterate through all subdirectories
            FileInfo[] Files = assetDirectory.GetFiles("*.prefab"); // Get all prefab files in asset's directory
            foreach(FileInfo file in Files) { // Iterate through all files in the subdirectory
                assetImporter = AssetImporter.GetAtPath(ASSETS_TO_BUNDLE_PATH + @"\" + assetDirectory.Name + @"\" + file.Name); // Attempt to get asset importer
                if(assetImporter != null) { // If the assetImporter doesn't work, skip
                    assetImporter.SetAssetBundleNameAndVariant(file.Name, ASSET_BUNDLE_VARIANT); // Mark asset (.prefab) to be bundled
                    assetImporter.SaveAndReimport(); // Save and reimport the asset
                }
            }
        }        
    }
    // Comment out method when not being used //
}