Mother and one close to her in family tree (6)
I believe the answer is:
damson
'family tree' is the definition.
'damson' can be an answer for 'tree' (damson is a type of tree). I'm not certain of the 'family' bit.
'mother and one close to her' is the wordplay.
'mother' becomes 'dam' (female parent of an animal).
'and' means one lot of letters go next to another.
'one close' becomes 'on' (I've seen this in other clues).
'to' is a charade indicator (letters next to each other) (I've seen this in other clues).
'her' becomes 's' (I can't explain this - if you can you should believe this answer much more).
'on' after 's' is 'son'.
'dam'+'son' is 'DAMSON'.
'in' is the link.
(Other definitions for damson that I've seen before include "Small stone-fruit for nomads" , "Small fruit for nomads" , "Kind of plum for nomads" , "Ma, Don's a fruit" , "Small purple plum" .)