If it works i see no issue. I wouldn't advise putting the ballast box on the ground though. It'll be better protected if mounted on the tree or if you dont want to drill into the tree, hammering a small piece of wood about 4ft long or so and mounting the box on that would work. I would urge you to use a cord length appropriate for what you're using it for. There's no need to have a cord that long. You should be fine with a 35W lamp but for higher wattages a longer cord will get too much stress if it's too long.

I understand what you mean about the ballast box being mounted up off the ground and I would do that if I had it out for more than a night. But I am big into easy to put up, take down and transport because my family has gatherings at many different places throughout the year and they ask me to do lighting for them and I want it to be easy to put up, take down and transport lol. Also I would not use a 25foot cord, like I said this is just a test, I would definitely use a smaller one! With the 35watt 25feet is okay at max? So what would be okay with 50watt? 15feet? 10feet? Thanks.

As long as it's not permanet you're fine then. For the actual power supply (meaning the cord that powers the ballast and lamp) you could probably use up to 50 feet with no problem (is that the cord you meant?)

As for the cord that connects the lamp to the ballast, you may not want to go more than 15 feet though because there's more than 120V going to the lamp and that can ruin the cord. If the cord is rated for 125V or 250V, i wouldn't recommend using it. I'd use individual conductors that can be bought at Lowe's (you'd need one conductor (wire) for each wire in the cord currently) for roughly a dollar a foot. I'd use either 12 gauge or 18 gauge wiring; which ever is used on the balalst leads. Hope this helps. I'm not an expert nor do i know every rule in the code book but if it's just for temporary use you can probably get by a little easier.

How many volts does a 35watt HPS ballast put out? And how many volts does a 50watt HPS ballast put out? I think its 55volts or something like that because doesn't it say that on the igniter? I could be totally wrong though...

I don't know. Jace would though.

I guess I answered it for myself... I found a nice chart in one of AEL catalogs titled "HPS Servicing Guide".
35watt: New lamp voltage range: 46-62volts End of life: 84volts Amps: .83
50watt: New lamp voltage range: 46-60volts End of life: 84volts Amps: 1.18
So I think anything rated for 120volt 15amp should be fine!

Ahh okay then you'll be fine. BTW, this is a very clever yet basic design. I like it. I love simple lights that get the job done and still look good by day and night.