You can use logs to build wooden pillars. They can be built to any height, but anything over four voxels high will require stairs so your Bricktrons can reach the blueprints.

To get logs, you first create a Harvest Task, either by holding down the right mouse button, or by clicking the "New Task" Button on middle left of your screen. Then you place it over some trees, and make sure it covers the amount of trees you want to harvest, by dragging the edge of the circle.

A Stockpile can hold 4 Logs. You can turn Logs into Planks in the Chopping Block.