Oak, eg (4)
I believe the answer is:
tree
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">oak eg</span>' is the definition.<br/ ><span class="explanation-format__explanation">(oak is a kind of tree)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for tree that I've seen before include "Elm, perhaps" , "Ash, chestnut, or araucaria, for example" , "Box or bay maybe?" , "elder, maybe" , "Shakespearean actor" .)