'treed' is the past tense/past participle of 'tree'. 'Tree' originates from Old English 'treow' (or 'treo'), from Proto-Germanic '*trewwiz', ultimately from Proto-Indo-European '*deru-' meaning 'hard, firm; oak'.

'tree' appeared in Old English as 'treow'/'treo', developed into Middle English forms like 'tre(e)', and eventually became the modern English word 'tree'; the verb 'to tree' (to force into a tree) developed from the noun in later usage (notably in hunting contexts).

Initially it meant 'a tree, wood, or something hard/firm'; over time the noun sense remained while a verbal sense—'to drive or force (an animal) into a tree'—developed, giving the past/p.p. form 'treed' used in hunting and figurative contexts.