fighting tree fires

Burn it when its on the ground. You can control a fire on the ground, and its not in the canopy of the forest making it easier to bounce from tree to tree.

As with all fires it depends. If the fire has been burning for some time it may have burnt out the inside of the tree this makes it very dangerous to fall the tree. burnt out branches or the whole tree may come crahing down (widow makers) at any time without warning.
If the tree fire is sending out sparks (roman candle) and the weather conditiond demand it. the tree may well need to come down.
If the weather conditions are suitable let the tree burn standing up. The fire may well burn itself out but make the area very safe by roping off and signage.
If the tree need to come down, sound the stem with an axe to determine if it is hollow. Clear at least two escape routes of brush and ground debrid away from the tree base.
Be prepared to sacrifice your chainsaw if this tree is burnt out it may come down in a hurry. leave the saw and move away as swiftly as possible.
keep one eye on your saw cut (so you can see movement) and the other eye on the crown as branches will almost certainly come down.

Is it easier to extinguish a tree fire on the ground Yes it is but getting the tree on the ground may be more difficult than you imagine.
this is a job best left to professional firefighters or fallers.

dadpad,
You answered the question exactly the same way I would have.
As a firefighter, I would rather the tree was on the ground (its easier and safer), but we dont always have that option.