Trees was born on 12 June 1946,[1] in Middlesbrough and spent his childhood in Scunthorpe, North Lincolnshire.

In 1994, he was made Professor of veterinary parasitology[1] and appointed Head of the Parasite and Vector Biology Division at the Liverpool School of Tropical Medicine.

[9] In March 2016 Trees was elected an Honorary Fellow of the Royal Society of Edinburgh, the RSE's highest class of Fellowship.

[10] On 3 July 2012, Trees was made a life peer as Baron Trees, of The Ross (a road[11] in Comrie in Perth and Kinross),[12] and was introduced in the House of Lords on 12 July 2012,[13] where he sits as a Crossbench, or independent, peer.

[14] Baron Trees made his maiden speech in the House of Lords in January 2013 on the Leveson debate.