'tree-filled' originates from English, specifically the combination of the noun 'tree' and the past-participial adjective 'filled', where 'tree' originates from Old English 'treow' meaning 'tree' and 'fill' (from which 'filled' derives) originates from Old English 'fyllan' meaning 'to make full'.

'tree' changed from Old English 'treow' (later Middle English forms like 'tre(e)') and 'fill' came from Old English 'fyllan' (Middle English 'fillen'); the compound adjective 'tree-filled' is a modern, transparent formation joining these elements.

Initially the roots meant 'tree' and 'to make full'; over time the compound came to mean 'filled with trees' in the simple adjectival sense.