Gibbon lives up a tropical fruit tree, mostly (7)

'gibbon lives up' is the definition.
I can't tell whether this defines the answer.

'a tropical fruit tree mostly' is the wordplay.
'a tropical' becomes 'sia' (I can't justify this - if you can you should give a lot more credence to this answer).
'fruit tree' becomes 'mango' (mango is a kind of fruit tree).
'mostly' means to remove the last letter (most but not all of the word).
'mango' with its last letter taken away is 'mang'.
'sia'+'mang'='SIAMANG'

Can you help me to learn more?