Please help me to review my IELTS essay

The diagram illustrates the process in which pencils are produced.

There are 10 main stages in the process of manufacturing pencils, beginning with replanting small trees and ending with painting, sharpening and stamping pencils.

At the first stage of the process, small trees are grown in 3 months before they are replanted, and the replanted trees are grown in 3 years before they are thinned. Those thinned trees are grown in 14 years before being cut down to collect timber. Next, this timber is cut to create thin slats.

At the following stage of the process, those slats are treated. 60 days later, some grooves are created in one face of a treated slat, and then glue and black lead are put into these grooves. After that, a new slat is put above before two slats are hard-pressed and heated to create a block, which is cut to produce raw pencils. The last step of the process is that the raw pencils are painted, sharpened and stamped to be ready for sell.