In the Logos* section, you can specify a list of images that will alternate one after another with the parameters chosen in the Splash Screen section:
Personal versus Plus versus Pro and Enterprise Unity editions: when building your
game with the personal version of Unity, you should be aware that a "Made with Unity"
splash screen will be shown before your game loads. Unity Plus, Unity Professional,
and Unity Enterprise users will be able to set up their own graphics for the animation,
without the Unity logo, and, if they want, disable the intro completely by deselecting
the Show Unity Logo checkbox.