The use of evergreen trees to celebrate the winter season occurred before the birth of Christ.
The first decorated Christmas tree was in Riga, Latvia in 1510.
The first printed reference to Christmas trees appeared in Germany in 1531.
Besides evergreens, other types of trees such as cherry and hawthorns were used as Christmas trees in the past.
Using small candles to light a Christmas tree dates back to the middle of the 17th century.
Thomas Edison's assistant, Edward Johnson, came up with the idea of electric lights for Christmas trees in 1882. Christmas tree lights were first mass-produced in 1890.
In 1900, large stores started to erect big illuminated Christmas trees.
The tradition of an official Chicago Christmas tree was initiated in 1913 when one was first lit by Mayor Carter H. Harrison in Grant Park.
The official Christmas tree tradition at Rockefeller Center began in 1933. Since 2004 the tree has been topped with a 550-pound Swarovski Crystal star. And since 2007, the tree has been lit with 30,000 energy-efficient LED's which are powered by solar panels.
Every year since 1947, the people of Oslo, Norway have given a Christmas tree to the city of Westminster, England. The gift is an expression of good will and gratitude for Britain's help to Norway during World War II.
Since 1971, the Province of Nova Scotia has presented the Boston Christmas tree to the people of Boston, in gratitude for the relief supplies received from the citizens of Boston after a ship exploded in 1917 following a collision in the Halifax, Nova Scotia Harbor. Part of the city was leveled, killing and injuring thousands.

Every year since 1947, the
people of Oslo, Norway have
given a Christmas tree to the
city of Westminster, England.
The gift is an expression of
good will and gratitude for
Britain's help to Norway
during World War II.
Since 1971, the Province of
Nova Scotia has presented the
Boston Christmas tree to the
people of Boston, in gratitude
for the relief supplies received
from the citizens of Boston
after a ship exploded in 1917
following a collision in the
Halifax, Nova Scotia Harbor.
Part of the city was leveled,
killing and injuring thousands.

how come all the christmas tree gifts are associated with the world wars?

The boston christmas tree was presented by halifax in 1918, not 1971!