For the time being, the only way to add activities in bulk is with an import.
Adding activities in bulk for new items
If you wish to add activities in bulk for new People, Organizations, or Deals, make sure to add the activity information in your spreadsheet. During the mapping, you will be able to link your activity information with the Pipedrive activity fields. The import will create new contacts and will add activities linked to those contacts.
Adding activities in bulk for existing items
If you already have People, Organizations or Deals in your Pipedrive account and wish to add activities for them in bulk, we suggest utilizing the Pipedrive System ID function when importing a spreadsheet.
To obtain a spreadsheet with the People, Organization or Deal IDs, we suggest going to the List View and adding the Pipedrive System ID columns. To add columns to your List View, click on the gear icon and choose the correct columns.
Once that column is visible, export the filter results to a spreadsheet:
Then provide the necessary activity information in the spreadsheet that you just exported, and import that spreadsheet back into your Pipedrive account, mapping the activity fields accordingly. Once the import is finished, activities will be created for every item that was exported.
For more information on how to import data into Pipedrive with spreadsheets read this article.