The same thing is happening to me!
After days & days of trying I finally got my E-trees back, although I've lost my daily streak and have to start over and I still have to complete 40 thousand points to plant my next Tree. When I look at my total score/points, you can clearly see I've planted 41 trees. But it's only showing I've planted 39 trees.
I hope this helps others who were signed out and couldn't sign back in again.
Sign into your email address.
Step 1 - Click on Bing (top right-hand side, that is where mine is
Step 2 - Click on the little E-tree and complete the tasks. It's a new mini-E-tree program that only goes for 7 days.
Step 3 - Click on Sign in via Bing and manually put in your email address and password!
That's what I did and got my E-trees back. I'm really annoyed that I have lost my daily streak and have to start over again, which takes 7 days to get back to 500 bonus points.
What a headache!!!