Tree with large span (5)
I believe the answer is:
larch
'tree' is the definition.
(larch is a kind of tree)
'with large span' is the wordplay.
'with' means one lot of letters go next to another.
'large' becomes 'L' (eg in clothes sizes).
'span' becomes 'arch' (I've seen this before).
'l'+'arch' is 'LARCH'.
(Other definitions for larch that I've seen before include "Supplier of timber" , "wood" , "Coniferous tree with deciduous bright green needles" , "Deciduous conifer" .)