Hypersensitivity Pneumonitis (HP): Given the patient's history as a retired electrician, exposure to various antigens such as dust, molds, or chemicals is plausible. The slightly peri-lymphatic and tree-in-bud distribution, more pronounced in the upper lobes, is consistent with HP, especially in a never smoker.

Sarcoidosis: This condition often presents with a micronodular pattern on imaging, particularly in the upper lobes, and can have a peri-lymphatic distribution. The tree-in-bud pattern can also be seen in sarcoidosis, although it's less common.
Silicosis or Coal Worker's Pneumoconiosis (CWP): Although the patient is a retired electrician, exposure to silica or coal dust could have occurred, leading to these conditions. Both can present with upper lobe predominant micronodular patterns.
Berylliosis (Chronic Beryllium Disease, CBD): Given the patient's occupation, exposure to beryllium is possible. CBD can present similarly to sarcoidosis on imaging, with a micronodular pattern and upper lobe predominance.

Tuberculosis (TB): Although less likely in a never smoker without a known exposure history, TB can present with a tree-in-bud pattern and should be considered, especially if the patient has traveled to or lived in areas with high TB prevalence.
Fungal Infections (e.g., Histoplasmosis, Cryptococcosis): These can mimic other diagnoses and are critical to identify due to their potential for severe disease and the need for specific antifungal treatment.
Malignancy (e.g., Lymphangitic Carcinomatosis): While less common, malignancies can present with a peri-lymphatic distribution and should be considered, especially if there are other symptoms or risk factors present.

Langerhans Cell Histiocytosis (LCH): This condition can present with a variety of pulmonary findings, including micronodular disease, but is relatively rare and often associated with other systemic findings.
Pulmonary Alveolar Proteinosis (PAP): Although it typically presents with ground-glass opacities, PAP can have a variety of appearances and should be considered in the differential diagnosis of diffuse lung disease, especially if other findings are present.
Rare Pneumoconioses (e.g., Hard Metal Disease, Tungsten Carbide Disease): Depending on the patient's specific occupational exposures, other rare pneumoconioses could be considered, though they are less likely without a clear exposure history.