Sidetracking a wellbore without milling a window

A method comprising:

• forming a primary wellbore through a subterranean zone using a wellbore drilling assembly;
• casing at least a portion of the primary wellbore;
• installing a whipstock within the primary wellbore at a depth;
• and
• using the wellbore drilling assembly and the whipstock, and without using a milling assembly, drilling a window through a side wall of the casing to form a lateral wellbore from the primary wellbore.

A well tool assembly comprising:

• a wellbore drilling assembly configured to form a primary wellbore through a subterranean zone;
• a casing configured to be installed within the primary wellbore;
• a bottom hole assembly configured to be installed within the casing, the bottom hole assembly comprising:
• a whipstock configured to be installed within the primary wellbore,
• a tubular assembly configured to be installed within a primary wellbore formed by the wellbore drilling assembly, the tubular assembly comprising:
• a stationary tubular comprising a wall, a portion of the wall made of a soft material, the stationary tubular formed as an outer layer of the tubular assembly, and
• a moving tubular formed as an inner layer of the tubular assembly, the moving tubular configured to translate relative to the stationary tubular to cover or expose the soft material;
• and
• a shifting tool configured to engage the moving tubular and to translate the moving tubular relative to the stationary tubular until the soft material is exposed, wherein the whipstock is configured to guide the wellbore drilling assembly to drill through the soft material and to drill a lateral wellbore from the primary wellbore.