What's the best way to anchor a 7' Christmas tree to the bottom of the lake?

I was thinking of drilling a hole in the base and running wire through it and then wrap the wire around a cinder block at the base and drop the tree over to let it sink. The base is about 4'to 5" thick and I was wondering if only one block would hold it down.

Also is it better to have them standing up or laying on their side?

I have about ten trees to put out. How many should I put in each area I want the fish to gather? I will be dropping them near drop offs close to creek channels in about 15' to 20' of water.

Any ideas or suggestions are helpful.