The distance seen when one is in large, deciduous tree up there (4)
I believe the answer is:
mile
'the distance' is the definition.
(mile is a unit of distance)
'when one is in large deciduous tree up there' is the wordplay.
I cannot really see how this works, but
'when' could be 'e' (I've seen this in other clues) and 'e' is present in the answer.
'one' could be 'i' (Roman numeral) and 'i' is found in the answer.
'large' could be 'l' (eg in clothes sizes) and 'l' is located in the answer.
A single letter 'm' remains which might be clued in a way I don't understand.
This may be the basis of the clue (or it may be nonsense).
'seen' is the link.
Can you help me to learn more?
(Other definitions for mile that I've seen before include "1.61km" , "'1,760 yards (4)'" , "Distance race" , "Unit of distance" , "Measure" .)