Maybe, maybe not.
It is natural for trees to lean. Most of the time, the lean is phototropic: the tree is trying to get as much sunlight as possible.
The possibility that a leaning tree will fall over depends on a combination of many factors, such as:
- The angle of the lean
- Whether the tree is growing extra support to hold itself up
- Whether there are defects in the trunk or roots
- Whether the branch structure is unbalanced.
If you're concerned that your leaning tree is dangerous, call a Certified Arborist who can assign the tree a risk level. This will help you decide whether or not it should be removed.