Take a breath, having almost bisected base of tree (6)
I believe the answer is:
inhale
'take a breath' is the definition.
(inhaling is a kind of taking a breath)
'almost bisected base of tree' is the wordplay.
'almost' means to remove the last letter (most of the word but not all of it).
'bisected' becomes 'in half' (I've seen this in another clue).
'base of tree' becomes 'e' (I can't justify this - if you can you should give a lot more credence to this answer).
'inhalf' with its last letter taken away is 'inhal'.
'inhal'+'e'='INHALE'
'having' is the link.
Can you help me to learn more?
(Other definitions for inhale that I've seen before include "Draw in air or smoke" , "Draw air into lungs" , "Take smoke into the lungs" , "Breathe in (gas, smoke)" , "Whiff" .)