Import Assets and Packages in Unity all at once.

ImportAssets.cs

using System.Collections.Generic;
using System.IO;
using UnityEngine;
using UnityEditor;
using UnityEditor.PackageManager.Requests;
using UnityEditor.PackageManager;

// Place this script in YOUR_PROJECT_FOLDER/Assets/Editor
// Run this script by clicking on the Importer menu item below the Unity title bar (File, Edit ... Importer)
public class ImportAssets : EditorWindow {
    static string unityPackagesPath = "C:/Users/user/Downloads/UnityAssets";

    static AddRequest Request;
    static int index = 0;

    // Add the packages you want to install here.
    // Package versions and names can be obtained by opening the package manager
    // then clicking on the package you are interested in and clicking on "view changelog"
    // A browser window will open with a URL similar to the following:
    // https://docs.unity3d.com/Packages/[email protected]/changelog/CHANGELOG.html
    // Obtain the name and the version from the string between Packages/ ... /changelog
    // Omitting the version will install the latest version available.
    // Specific versions can be installed by adding the version after the package name:
    // [email protected]
    // package.name@version
    static List<string> packages = new List<string> {
        "com.unity.textmeshpro",
        "com.unity.shadergraph",
        "com.unity.visualeffectgraph",
        "com.unity.terrain-tools",
        "com.unity.polybrush",
        "com.unity.postprocessing",
        "com.unity.cinemachine"
    };

    [MenuItem("Importers/Asset Importer")]
    public static void ImportAllAssets() {
        string[] unityPackages = Directory.GetFiles(unityPackagesPath);

        for(int i = 0; i < unityPackages.Length; i++) {
            if(unityPackages[i].EndsWith(".unitypackage")) {
                AssetDatabase.ImportPackage(unityPackages[i], false);
            }
        }

        Debug.Log("Assets have been imported");
    }

    // Example of a for loop through methods rather than the for loop built into the language.
    [MenuItem("Importers/Smart Package Importer")]
    public static void SmartImportAllPackages() {
        if(index >= packages.Count) { return; }

        Request = Client.Add(packages[index]);
        EditorApplication.update += Progress;

        index++;
    }

    static void Progress() {
        if(Request.IsCompleted) {
            if(Request.Status == StatusCode.Success)
                Debug.Log("Installed: " + Request.Result.packageId);
            else if(Request.Status >= StatusCode.Failure)
                Debug.Log(Request.Error.message);

            EditorApplication.update -= Progress;

            if(index >= packages.Count) {
                Complete();
            } else {
                SmartImportAllPackages();
            }
        }
    }

    static void Complete() {
        Debug.Log("Completed importing all packages.");
        Request = null;
        index = 0;
    }

    [MenuItem("Importers/Dumb Package Importer")]
    public static void DumbImportAllPackages() {
        // NOTE: This will freeze the editor. Please wait until the process has completed.
        while(index != packages.Count) {
            Request = Client.Add(packages[index]);

            while(!Request.IsCompleted) {
                System.Threading.Thread.Sleep(2000);
            }

            if(Request.Status == StatusCode.Success)
                Debug.Log("Installed: " + Request.Result.packageId);
            else if(Request.Status >= StatusCode.Failure)
                Debug.Log(Request.Error.message);

            index++;
        }

        Complete();
    }
}