Ctrl + Shift + N will open a new window, while Ctrl+K then releases the keys, and pressing O would open the current tab in a new window. You can then use menu File → Open Folder to have two instances of Visual Studio Code with different folders in each window.
⌘ + Shift + N and ⌘ + K for For Mac.:
- ⌘ + Shift + N (Open new Window)
- ⌘ + K then release the keys and press O (open current Tab in new Window)
List of helpful keyboard shortcuts can be found here.