Here is a ruling from IslamQA:
The Christmas tree is one of the symbols of the Christian festival and celebration; this is why it is named for Christmas. It is said that it was first officially used as a symbol in this manner in the sixteenth century in Germany, in the Cathedral of Strasbourg in 1539 CE.
It is not permissible to imitate the kuffaar in any of their acts of worship, rituals or symbols, because the Prophet (blessings and peace of Allah be upon him) said: “Whoever imitates a people is one of them.” Narrated by Abu Dawood, 4031; classed as saheeh by al-Albaani in Irwa’ al-Ghaleel, 5/109
So it is not permissible to put up this tree in a Muslim house even if you do not celebrate Christmas, because putting up this tree comes under the heading of imitating others that is haraam, or venerating and showing respect to a religious symbol of the kuffaar….
“Zayn Malik’s family receive ‘disgusting’ death threats – over a CHRISTMAS TREE,” by Jerry Lawton, Daily Star, December 10, 2016:
THE family of Zayn Malik got death threats from Muslim fanatics after his teen sister tweeted a photo of a Christmas tree.
The extremists accused the family of “insulting Islam” and warned of “retribution”.
Former One Direction singer Zayn celebrates Christmas as well as Muslim festivals such as Eid because he hails from a dual-faith family.
While dad Yaser follows Islam, mum Trisha was born a Christian.
But after sister Safaa posted a snap of the tree at their home in Bradford, West Yorks, she was blitzed with vile comments.
They branded the family’s celebration of Christmas “an insult to Islam” and said they were “a disgrace to the faith”.
They also made sinister threats to the Maliks….