Becoming comfortable in the deep end & treading water

Question
QUESTION: Hi, I'm an adult who's been learning how to swim, had some  lessons (which are now finished) and it went well, I can do back-stroke/front crawl reasonably well. However, when I go to the pool and do lengths I have to stop before the water is too deep to stand up, because I can't tread water. Is it possible to be comfortable in the deep end without being able to tread water? (My instructor said it wouldn't be long before I was comfortable in the deep end). I.e, perhaps by just knowing how to float (on your back) and
swim?

What's the best way of learning to tread water? At the moment I can stay afloat in a horizontal position (on my back) doing breast stroke legs, but when I try that in a vertical position, or the bicycle-riding/circular kicks, I just sink. Does it count as treading water if you're horizontal?

ANSWER: No, that's just floating.  Treading water is vertical.  Try using a frog kick or large flutter kicks instead.  The best kick to use is an eggbeater kick(more like an alternating frog kick[one leg at a time}).  
The fear of deep water will go away as you get more comfortable in the water.

---------- FOLLOW-UP ----------

QUESTION: Hi, thanks for your answer.

So do you think I should try to learn to tread water *in order to* become comfortable in deep water, or wait until I'm comfortable in deep water *before* trying to learn to tread water.

I.e. either (a) swim 3/4 lengths and try to learn to tread water when in the deep-ish bit, or (b) just swim 3/4 lengths, and maybe practice floating, until I'm happy doing full lengths. (Don't know if (b) is possible)

cheers.

Answer
Hello again--
First a quick question, can you start swimming in the deep end?
If you can then it's a little easier to aim for the shallow end then to know that you have the deep end to contend with.
I think you should work on swimming the length of the pool, if possible next to a wall, that way if you run out of energy or panic you have something to grab onto.  Treading water can also be done next to an edge for the same reason.  Comfort in deep water comes with being in deep water, the best way to conquer a fear is to face it.  The more you work at it the easier it gets.  The same goes for treading water, the more you work at it the better you get, but like I said try to stay near a side of the pool so you have somewhere to reast if you get nervous or tired.
Good luck,
George