Yeah, but the metals don't come together to produce a terrain object like a tree. They spawn as ores, and get processed into dusts, bars, nuggets, tools etc.
Perhaps they could be classified as structures like the Infernal Furnace.
The way I see it the tree articles have a few big problems.
1. This wiki is mostly focused on items, so putting information about the tree itself in its items pages seems awkward and out of place. Yet we have almost no articles about trees themselves save that bad general tree article.
That sounds more of a problem of the wiki than with the trees.
2. Most tree item pages are not very exciting or unique, hence little effort goes into writing them, and many do not get written at all.
I would say half or more of trees nowadays are more "exciting" than Vanilla trees.
Special new textures for old recipes (new texture doors and workbenches and such), special biomes or spawn rates, certain entities that spawn WITH them, and even some trees that are literally explosive or upside down.
3. Unlike metals, most tree items can be used interchangeably in crafting, so there is a lot of repetitious information if we put every use for Wood in each type of tree's wood article. Not to mention keeping them all updated would be a nightmare.
As I've said several times elsewhere, we need to start assigning people to positions, I said elsewhere assigning people to specific modpacks but I can see having people in charge of trees due to this issue. Wiki Projects are what this is usually called and we definitely could use tons of these.
Personally I guess I'm leaning towards having a generic article on Leaves, Wood, Planks and Saplings that covers in detail all of their usage in crafting in machines, while each type of a tree has an article that covers its unique characteristics (height, amount of saplings needed to grow, biomes etc.) and having brief sections that have the item boxes for its particular leaves, wood, planks and saplings.
That seems... unorthodox...
A lot can change from tree to tree, sometimes when you break certain woods something else drops with it, some certain woods are used with tools to produce items, some leaves drop unusual items, some leaves have graphical changes that indicate when an unusual item can be dropped, and some leaves spawn foods that just grow down from them that you can break off and regrows.