See https://hawksey.info/blog/2024/07/automate-google-drive-test-data-creation-with-google-apps-script/

Code.gs

function createDummyFoldersWithNesting() {
  // Get the starting point for the dummy folder structure
  // Replace with your desired folder ID or use 'root' to start in the root of your My Drive
  const rootFolder = DriveApp.getFolderById("YOUR_FOLDER_ID"); 

  // Configuration for the dummy structure
  const maxNestingLevel = 3;        // How many levels deep the structure will go
  const maxFoldersPerLevel = 5;     // Maximum number of folders to create in each level
  const maxFilesPerFolder = 5;      // Maximum number of files to create in each folder
  const fileFolderPrefix = 'Dummy'  // Text added to the start of all folders/files

  // ---------------------------- //

  // Array of file types we want to create (Documents, Sheets, Slides)
  const fileTypes = ["document", "spreadsheet", "presentation"];
  
  // Function to randomly pick a file type from the array
  const randomFileType = () => fileTypes[Math.floor(Math.random() * fileTypes.length)];

  // Recursive function to create nested folders and files
  const createNestedFolders = (parentFolder, currentLevel) => {
    // Decide how many folders to create in this level
    const numFolders = Math.floor(Math.random() * maxFoldersPerLevel) + 1; // Randomly create 1-5 folders
    console.log(`Creating ${numFolders} folders in ${parentFolder.getName()} (level ${currentLevel})`);

    // Create folders and files within them
    for (let i = 0; i < numFolders; i++) {
      const levelName = `${currentLevel}.${i + 1}`;    // Name for the folder (e.g., "1.2" for 2nd folder in level 1)
      const folder = parentFolder.createFolder(`${fileFolderPrefix} Folder ${levelName}`); // Create the new folder

      // Create files within the new folder
      Array.from({ length: maxFilesPerFolder }, (_, index) => {   // Create up to 5 files
        const fileType = randomFileType();                     // Pick a random file type
        const fileMetadata = {                                // Prepare information about the new file
          name: `${fileFolderPrefix} ${fileType[0].toUpperCase() + fileType.slice(1)} ${levelName}.${index + 1}`,  // File name (e.g., "Dummy Document 1.2.3")
          mimeType: `application/vnd.google-apps.${fileType}`, // Google Apps Script file type (document, spreadsheet, or presentation)
          parents: [folder.getId()]                           // Place the file in the newly created folder
        };
        Drive.Files.create(fileMetadata, undefined, { supportsAllDrives: true }); // Create the file in Google Drive
        console.log(`  Created ${fileType} in folder ID: ${folder.getId()}`);
      });

      // Recursive call: If haven't reached max nesting level, create more folders in this one
      if (currentLevel < maxNestingLevel) {
        createNestedFolders(folder, currentLevel + 1);
      }
    }
  };

  // Start the process
  console.log("Starting dummy folder creation...");
  createNestedFolders(rootFolder, 1);
  console.log("Finished creating dummy folders!");
}