A Christmas tree and a toddler can be a bad combination. There are a bunch of different solutions that have been used successfully.
We've had good success by getting a teeny little tree and putting it up on a table. The toddler couldn't reach it, but we could. Not much room for stacking gifts, but then you have a built-in reminder to stay prudent with gift-purchasing.
You could also put the tree inside a playpen, if you have one, or block it off with gates or a playard.
Other people have strung wires from walls or ceilings to anchor the tree and prevent it from toppling, or to suspend the tree upside-down. (I have to confess that I don't really get the point of this.) This seems to work really well to keep the tree upright, but you still have the problem of kids pulling off ornaments, lights, and branches.
What do you do? And at what age did the tree cease to be a negative temptation for your child? In our house, 21 months seems to be the cut-off between total tree destruction and pointing wide-eyed.