The word "桦树" is formed by combining the character "桦", which uses the semantic component "木" (meaning "tree") and the phonetic component "华" (suggesting its pronunciation), with the character "树", meaning "tree", which also incorporates the semantic component "木" to reinforce its meaning; together, they create a compound word where "桦" specifies the birch type and "树" denotes the general plant category, resulting in the term for birch tree.