diff --git a/src/blobset.nim b/src/blobset.nim
index 9937ce0..879297f 100644
--- a/src/blobset.nim
+++ b/src/blobset.nim
@@ -218,7 +218,7 @@ proc getSet(env: Env; path: string): BlobSet=
   result = env.sets.getOrDefault(path)
   if result.isNil:
     result = newBlobSet()
-    result.insertPath(env.store, pcDir, path)
+    result.insertPath(env.store, path.getFileInfo.kind, path)
     if not result.isEmpty:
       env.sets[path] = result
 
@@ -443,15 +443,10 @@ proc keyFunc(env: Env; args: NodeObj): NodeRef =
   args.atom.str.toKey.newAtom.newNode
 
 proc ingestFunc(env: Env; args: NodeObj): NodeRef =
-  let set = newBlobSet()
+  var bs = newBlobSet()
   for n in args.walk:
-    returnError n
-    let a = n.atom
-    case a.path.getFileInfo.kind
-    of pcFile, pcLinkToFile:
-      result = newNode(newAtomError("not a directory"))
-    of pcDir, pcLinkToDir:
-      result = newNode(newAtom(env.getSet(a.path)))
+    bs = env.store.union(bs, env.getSet(n.atom.path))
+  result = bs.newAtom.newNode
 
 proc blobFunc(env: Env; args: NodeObj): NodeRef =
   assertArgCount(args, 1)
diff --git a/src/blobsets.nim b/src/blobsets.nim
index 94dc5ed..a97f09e 100644
--- a/src/blobsets.nim
+++ b/src/blobsets.nim
@@ -209,6 +209,20 @@ func compactIndex(t: BlobSet; x: Key): int =
 func masked(t: BlobSet; x: Key): bool =
   ((t.bitmap shr x.sparseIndex) and 1) != 0
 
+proc apply*(bs: BlobSet; cb: proc (leaf: BlobSet)) =
+  ## Apply a callback to each set element.
+  for node in bs.table:
+    case node.kind
+    of hotNode:
+      apply(node, cb)
+    of leafNode:
+      cb(node)
+    else:
+      raiseAssert("cannot apply to node type " & $node.kind)
+
+func isEmpty*(s: BlobSet): bool = s.bitmap == Key(0)
+  ## Test if a set is empty.
+
 func nodeCount*(bs: BlobSet): int =
   ## Count of internal nodes in set.
   result = 1
@@ -266,13 +280,13 @@ func insert(t, l: BlobSet; depth: int) =
     t.bitmap = t.bitmap or (Key(1) shl key.sparseIndex)
     t.table.insert(l, t.compactIndex(key))
 
+func insert*(t, l: BlobSet) = insert(t, l, 0)
+  # Insert set node `t` into `l`.
+
 func insert*(t: BlobSet; name: string; blob: BlobId; size: BiggestInt) =
   ## Insert a blob hash into a trie.
   let leaf = BlobSet(kind: leafNode, key: name.toKey, blob: blob, size: size)
-  insert(t, leaf, 0)
-
-func isEmpty*(s: BlobSet): bool = s.bitmap == Key(0)
-  ## Test if a set is empty.
+  insert(t, leaf)
 
 func toCbor*(x: BlobSet): CborNode =
   const
diff --git a/src/blobsets/stores.nim b/src/blobsets/stores.nim
index 61f43da..ac8d89c 100644
--- a/src/blobsets/stores.nim
+++ b/src/blobsets/stores.nim
@@ -259,10 +259,13 @@ proc commit*(store: BlobStore; bs: BlobSet): BlobSet =
   let (id, _) = finish stream
   result = BlobSet(kind: coldNode, setId: id)
 
-proc union*(store: BlobStore; a, b: BlobSet): BlobSet =
-  ## Return the union of a set pair.
-  result = newBlobSet()
-  raiseAssert("not implemented")
+proc union*(store: BlobStore; sets: varargs[BlobSet]): BlobSet =
+  ## Return the union of `sets`.
+  let fresh = newBlobSet()
+  result = fresh
+  proc freshInsert(leaf: BlobSet) = insert(fresh, leaf)
+  for bs in sets:
+    bs.apply(freshInsert)
 
 # Store implementations
 #