What's a witch's broom?

Until today, I knew what it was, but didn't have a name for it. There's a white pine that doesn't look too healthy in my garden and that's suffering from this ailment.

The problem is caused by a fungus that produces a deformity in which the natural structure of the plant is altered. A dense mass of shoots grows from a single point, with the resulting structure resembling a bird's nest.

The one we're seeing is composed of healthy needles hiding a bunch of pine cones. The branch that holds looks like a skeleton, totally devoid of pine needles.

What concerns me is the durability of that seemingly weak branch. How long will it swings in the wind before it ruptures?