i need a lot of help with geo problem

so far i figured out that AT is angle bisector. im having trouble using angle bisector theorem or whatever else i need to use tho.

In an isosceles △ABC (AC = BC) its incircle touches the side BC at point T. Given AC = 4 and AT = 2. Find the length of AB.

Triangles ABC and ABT are similar.

AT = AB = 2