This problem is a variant of the problem of Unique Binary Search Trees.

I provided a solution along with explanation for the above problem, in the question "DP solution in 6 lines with explanation"

It is intuitive to solve this problem by following the same algorithm. Here is the code in a divide-and-conquer style.

```
public List<TreeNode> generateTrees(int n) {
return generateSubtrees(1, n);
}
private List<TreeNode> generateSubtrees(int s, int e) {
List<TreeNode> res = new LinkedList<TreeNode>();
if (s > e) {
res.add(null); // empty tree
return res;
}
for (int i = s; i <= e; ++i) {
List<TreeNode> leftSubtrees = generateSubtrees(s, i - 1);
List<TreeNode> rightSubtrees = generateSubtrees(i + 1, e);
for (TreeNode left : leftSubtrees) {
for (TreeNode right : rightSubtrees) {
TreeNode root = new TreeNode(i);
root.left = left;
root.right = right;
res.add(root);
}
}
}
return res;
}
```