重ねる and 束ねる: overlapping layers and a gathered bundle
Compare layering blankets with bundling flowers. Read the arrangement of the objects rather than only a change of wrapping material.
Layer the objects
重ねる, read かさねる, means layer or repeat. 寒いので毛布を二枚重ねた。 says that two blankets were layered because it was cold.
The arrangement concerns the two overlapping blankets. This differs from choosing material to wrap one object.
Gather a bundle
束ねる, read たばねる, means bundle. 庭で摘んだ花を十本ずつ束ねた。 says that the flowers picked in the garden were bundled in groups of ten.
十本ずつ is the flower count per bundle in this example. It does not make ten items a requirement for every use of 束ねる.
Preserve other contextual senses
小さな努力を重ねて技術を身に付けた。 says that someone repeated small efforts and acquired the skill. Here 重ねる concerns repeated action rather than physical layers.
In the selected object scenes, compare layers and bundles. That comparison does not exclude the repetition sense or other contextual uses of the verbs.
What arrangements are compared in 重ねた for two blankets and 束ねた for flowers?
Show the answer and why
Overlapping blanket layers and flowers gathered into a bundle, rather than merely different wrapping materials.