I'm not sure about national tree, the Oak would be a good candidate.
the Oak is an English emblem ... Scotland has The Scots Pine The question of UK emblems is very recent as each country within the treaty has there own emblems
National Democrats - United Kingdom - was created in 1995.
National Democrats - United Kingdom - ended in 2011.
The oak is the official national tree of the United States.
National Union of Students - United Kingdom - was created in 1922.
National Audit Office - United Kingdom - was created in 1983.
National Rifle Association of the United Kingdom was created in 1859.
A person that is a non UK national is a person who is not from the United Kingdom. If a person is from the United Kingdom that are considered to be a national of the country.
National Christmas Tree - United States - was created in 1923.
Poppy
A poppy.
yes
It could be said to be, as it is a very popular drink in the United Kingdom.