Is there a variant of Merkle tree with no traceability from root to leaves?
Merkel trees already allow you to decide how much you reveal. To prove presence of one leaf, you reveal it and the commits along its copath.

If your documents contain enough entropy then you do not need salts. If the documents do not, then you may prepend each document with a salt I.e. $\text{hmac}(\text{secret} \| \text{index}, \text{message})$.

The intermediate nodes do not need salts.

To avoid leaking the number of documents you can fix the copaths length to $\lceil\log_b(N)\rceil$. This adds an additional $N - b^{\lceil\log_b(N)\rceil}$ zero-sized documents as additional noise. $b$ is the number of branches per depth (usually $2$). The padding should be uniformly shuffled with all documents, not ordered or appended to the end. The $\text{index}$ identifier is the position from root-to-leaf left-to-right after flattening the tree. I.e. $[0], [1, 2], [3, 4, 5, 6]$.