How do I make a fading transition between animation

Hello everyone,

I am trying to make a 2d transition between animation.
What I mean by that is that I have an image that have an animator assigned to it, but instead of making a sharp transition between the animation, it will happen gradualy. Is there a way to do it without blend tree?

an example of what I want:
https://static.ezgif.com/images/fading-gif-creator-demo.gif

Thanks