Kudos to the kids and all that, but wouldn't a christmas tree covered with hairspray make it highly flammable?

I suspect the hairspray the seals the pine needles slowing the loss of moisture through the needles.

hairspray was a myth also experimented by Mythbusters in 2006, that is just 8 years ago. testing preexisting popular knowledge

While awesome that kids are doing science hairspray is not new. It's been used for long enough that it was one of the "mythical" solutions that the Mythbusters used to prolong tree life in a Christmas episode a year or two ago.
Reference: http://mythbustersresults.com/special10
You can keep needles from falling off of the Christmas tree by adding hairspray.
plausible
Declared the winner for being both the best looking and among the best in terms of controlling needle loss, though the added flammability of the hairspray to the drying Christmas tree could increase the tree’s natural fire hazard risk.

Dried hairspray isn't flammable, at least not more than a tree made of dried pitch, needles and wood.
The flammability of hairspray comes from the alcohol delivering it.

But will hairspray keep my hair from falling out?

A pine tree is already very flammable, and the dried hairspray would probably not make it more so, but do the spraying outside...
Any sealing liquid spray would likely give the same results, but say goodbye to the nice piney scent.
Since adding sugar and aspirin to the water in flower vases prolongs their freshness, it should work for pines as well.
So, don't buy a dry tree, make sure you put it in water asap, set it up away from any source of heat, and you should have a Xmas tree that will last for three weeks and more!
Merry Christmas

As someone who hates to throw out the Christmas cheer, the trick we use to keep the Christmas tree alive is flat ginger-ale.
Keep feeding it fort-nightly and I guarantee your tree will be alive until at least March.
The sugar keeps it going I think, but make sure to use flat soda, as we've had early drop outs while using fresh carbonated soda. (Perhaps the carbonic acid is poisonous to fir trees?)
That being said, Bermuda (where I live) is still at 55% humidity and 70-odd degrees (21 C) so the hairspray trick (that probably keeps the water of the needles in) might still be necessary.
Further Reading: The film "Idiocracy" explores the effects of energy drinks on plants. Professor Angela Moles should have expected the trees to die.

Yeah the Hairspray thing My mother used to do until the lit cigarette incident in 1973. This is not new.

Hairspray? I thought that was a movie...