Difficult to choose just five, but here they are:
2. Birch - for its papery white slim trunk, the purplish twigs and neat leaves - the associations with Northern forests (Northumberland, Scotland, and North America), and Algonquin Indians (Longfellow's Hiawatha, Thoreau's Maine Woods etc), and Robert Frost's poem.
3. Scots Pine - each has a distinctive 'head', the trunks have a lovely warm colour, it is native to Britain (unlike other pines), good timber, and reminds me of Malcolm Saville's Lone Pine Club books and Shepherd's illustrations of the Enchanted Place in Winnie the Pooh.
4. Cedar of Lebanon - rather specific: a couple of trees in Somerset with smooth branches, horizontal near the ground, scented bark, flat umbrellas of leaves... best tree for lying on.
Because they epitomized summer in southern England and they are all dead... (all the big ones, anyway). Sob!