MongoDB: Tree Node Structure with Object-Maps instead of Collections - mongodb

Question

Using MongoDB for storage, if I wanted to represent a tree structure of nodes, where child nodes under a single parent always have unique node-names, I believe the standard approach would be to use collections and to manage the node name uniqueness on the app level:
Approach 1: Collection Based Approach for Tree Data
{ "node_name": "home", "title": "Home", "children": [
{ "node_name": "products", "title": "Products", "children": [
{ "node_name": "electronics", "title": "Electronics", "children": [ ] },
{ "node_name": "toys", "title": "Toys", "children": [ ] } ] },
{ "node_name": "services", "title": "Services", "children": [
{ "node_name": "repair", "title": "Repair", "children": [ ] },
{ "node_name": "training", "title": "Training"", "children": [ ] } ] } ] }
I have however thought of the following alternate approach, where node-names become "Object Map" field names, and we do without collections altogether:
Approach 2: Object-Map Based Approach (without Collections)
// NOTE: We don't have the equivalent of "none_name":"home" at the root, but that's not an issue in this case
{ "title": "Home", "children": {
"products": { "title": "Products", children": {
"electronics": { "title": "Electronics", "children": { } },
"toys": { "title": "Toys", "children": { } } } },
"services": { "title": "Services", children": {
"repair": { "title": "Repair", "children": { } },
"training": { "title": "Training", "children": { } } } } } }
The question is:
Strictly from a MongoDB perspective (considering querying, performance, data maintainability and data-size and server scaling), are there any major issues with Approach #2 (over #1)?
EDIT: After getting to know MongoDB a bit better (and thanks to Neil's comments below), I realized that both options of this question are generally the wrong way to go, because they assume that it makes sense to store multiple nodes in a single MongoDB document. Ultimately, each "node" should be a separate document and (as Neil Lunn stated in the comments) there are various ways to implement a hierarchy tree, as seen here: Model Tree Structures in MongoDB

Answer 1

I think this use-case is not good for Mongo DB, because:
there's(MongoDB 2.6) no compress algorithm (your documents will be too large)
Mongo DB use database-level locks (when you want one large document, all DB operations will be blocked)
it will be hard to index
I think better solution will be some relational DB for this use-case.