There are three syllables in Christmas tree (Christ mas tree)
their Christmas tree
The Pohutakawa is called New Zealand's Christmas tree because it is covered in red Flowers which bloom around Christmas time.
I believe you meant "How is Christmas celebrated?" It is celebrated with a Christmas tree (an evergreen tree) being put in your house, and decorating the tree with ornaments. Many people also hang strands of lights on the outside of their house. Gifts are put under the tree on the night of Christmas Eve (December 24th) and opened Christmas morning (December 25th).
yes
It is because Muslim people believe that Jesus was born under a Christmas tree
with a tree
Yes
Some people have a star or an angel on top of their Christmas tree.
The tree is traditionally given by the people of Norway
Each year since 1947, a Christmas tree has been given to the people of London from the people of Norway in gratitude for Britain's support for Norway during World War II. For many Londoners the Christmas tree and carol singing in Trafalgar Square signal the countdown to Christmas.
That is a matter of opinion. If people want to use Xmas when they write, it is acceptable, though a little offensive to some people. If people want to call a tree a "holiday" tree instead of "Christmas" tree or say "Happy Holidays" instead of "Happy (or merry) Christmas", it is their personal choice. Other than that, there aren't too many ways to change the word Christmas, other than renaming the holiday, and to me that should not be done.