In minecraft, can I put wood blocks on top of trees to make them grow larger?
No, but technically you can plant a tree using a dirt block on top of/inside another tree to grow another tree. This sort of expands the tree, but the second tree will grow normally (and requires the same conditions as a normal tree to grow), but with a little bit of work you can grow huge "trees" and prune them to your liking this way. The top tree will still grow leaves, but it might be a small tree and thus not as impressive. You can always replace/regrow a tree anywhere you want inside the 'base' tree though.
Remember you can also use Shears on Leaf Blocks ti collect them, and you can make your own tree manually with Leaf and Wood blocks, but they won't exhibit some of the properties of properly grown trees like natural branches.
You put four jungle saplings in square, and use bonemeal on it to make a huge tree, with vines. (This only works in a jungle biome.)
There are also some tricks to grow small trees or big trees. If you dig a 1-block hole and plant a sapling in it will make a big tree. Dig a two-block hole and plant a sapling in it and it will make a small tree.