If the window in the basement is required for safety access, move the new door elsewhere.

Not a pro. What kind of flooring do you have? I had a carpenter cut a new crawlspace access into the floor of a walk-in closet. The top of the access hatch door is engineered wood matching the closet floor. Previously the only access had been a small window. Then you can pour new cement where the window is (or leave it, although I wouldn’t want a window under the deck).

Thanks! Flooring is hardwood. Would you do wide steps vs a deck? apple pie, it’s actually a crawl space rather than basement So am wondering if it’s more cost effective to just relocate that instead of the slider door.

Either stairs or deck are going to require the tree be removed, you can't walk out into a tree. Maybe move the slider to the right, close up the left window.

Thanks for info. If you make a separate small wood porch deck that lifts away easily, you could leave the crawlspace access hatch there- there may be some code requirements for safety, so check first. Alternatively, adding a new back door somewhere else instead of the window location would be worth looking into.