Branch seen in river? Good heavens! (4,2)
I believe the answer is:
dear me
'good heavens' is the definition.
I know nothing about this answer so I can't judge whether this works.
'branch seen in river?' is the wordplay.
'branch' becomes 'arm' (synonyms).
'seen in' is an insertion indicator.
'river?' becomes 'Dee' (River Dee).
'arm' placed into 'dee' is 'DEAR ME'.
Can you help me to learn more?
(Other definitions for dear me that I've seen before include "Expression of dismay" , "Expression of mild regret from precious self" , "how distressing!" , "Mild expression of distress from expensive self" , "What a pity" .)