Hard sci-fi novel. Protagonist uses a wormhole portal and discovers a second version of herself (sister? clone?). May also feature tree-like alien life forms.
As suggested by user Handsome Jim and confirmed by the OP in comments above, this is Proxima (2013) by Stephen Baxter.
Per the blurb on the book's goodreads.com page:
The very far future: The galaxy is a drifting wreck of black holes, neutron stars, and chill white dwarfs. The age of star formation is long past. Yet there is life here, feeding off the energies of the stellar remnants, and there is mind, a tremendous galaxy-spanning intelligence each of whose thoughts lasts a hundred thousand years. And this mind cradles memories of a long-gone age when a more compact universe was full of light... The 27th century: Proxima Centauri, an undistinguished red dwarf star, is the nearest star to our sun. How would it be to live on such a world?