Has there been any serious studies into the relationship between the Asherah tree and the Christmas trees, with the possibility of the former being the source of the latter?
There is no historical connection.
The cultures that worshiped Asherah were mostly destroyed when the Babylonians invaded the kingdom of Judah and took a large portion of the populace as captives. The last reference to Asherah worship in the Bible is 2 Kings 23, during the reign of Josiah (r. 640 to 609 BCE).
Christmas trees became popular in Europe starting in Germany in the 1500s. There is no historical or cultural connection to the practices within Judah.
Well as far as I can see through many scripture in the old testament, the mention of the ASHERA tree is documented and is the consort of YHWH one the seventy sons of El. Basically the symbol of ASHERA was a tree or a cutting or formation of a pole or Tatum totum totim pole or tree of life and or knowledge or any wooden form of worship and sacrifices were made unto it. So when you put up your X mas tree you would have no understaning of its origen or myth by many different cultures which have been altered hence the word Alter. To change message and meaningful ness through time.
The garden of eden part of Genesis myth is possibly derived from the Asherah and other Mesopotamian myths. Not the Christmas tree, which has its origin in other pagan rituals.
In the Kuntillet 'Arjud and Khirbet el-Kom inscriptions, Asherah is named with Yahweh -- probably as his consort. In Canaanite myth, Asherah (Ug. Athirat) was the consort of El, the creator god, and she begat the seventy lesser gods, the sons of El. Asherah became Yahweh's consort through an identification of El with Yahweh (seen throughout the OT). In Canaanite texts, Asherah is called the "Mother of All" and one of her titles was qnyt 'ilm "Creator of the Gods". It is interesting that qnh is an unusual word in Hebrew for "create" as it usually means "acquire" (El, in contrast, was called bny bnwt "Creator of Created Things" in the Ugaritic texts). The notion of Eve as a creator goddess also appears in muted form in Genesis 3:20, 4:1 where Eve is called "the mother of all living" and Eve says after the birth of Cain, "I have created (qnh) a man with the help of Yahweh," employing the same verb as applied to Asherah in the Ugaritic texts. The latter quote is also very similar to a statement regarding the Akkadian creator goddess Aruru (= Sumerian Ninhursag):
Aruru zi-ir a-mi-lu-ti it-ti-shu ib-ta-nu
"Aruru, with the help of [Marduk], created the seed of mankind" (KIB, vi. I, 40).
Another clue that Eve's identity originally was not as it is given in the story can be found in the name: Hebrew chwwh, being related to Aramaic chwyh and Phoenician chwt "snake". Chawat appears in a Phoenician inscription as one of the names of Elat "Goddess", that is, Asherah.
It is in Proverbs where we meet Asherah as Wisdom personified. She appears as a creator goddess in Proverbs 8:22-31 and the following chapter describes a banquet that Wisdom hosts in her palace (Proverbs 9:1-6). In the Ugaritic texts, we read similarly of Asherah and her consort El hosting banquets in their mountain palace (cf. KTU 1.1 IV 26-35).
Proverbs 3:13-18 contains some paronomasia between the name Asherah ('ashrh) and the word "happy" ('ashre), which is paired with the "tree of life" in a chiasm:
"Happy ('ashre) is the one who finds wisdom .... She is a tree of life ('ts chyym) to those who lay hold of her; those who hold her fast are made happy (m'sshr)." (Proverbs 3:13, 18; cf. 11:30; 15:4)
The expression is nearly identical to "the tree of life" ('ts h-chyym) of Genesis 2:9, which refers to a specific mythological tree while the "tree of life" in Proverbs refers to a more abstract Wisdom, but the verse also plays on the name Asherah. It is interesting that Wisdom is identified with the "tree of life" when a "tree of knowledge of good and evil" (e.g. "wisdom") is distinguished from the Tree of Life in the Eden narrative. Many scholars since the time of Wellhausen have suggested that this second tree originated as a doublet of the first.