D3 Tree Graph Modified Data Model - d3.js

Question

I'm hoping to get opinions on what would be a good data model to drawing something like d3 tree graph. Tree graph won't work for me as is because I have scenarios where a child node could be linked with two parent nodes, sometimes, the parent nodes from different levels of hierarchy. I'm planning to modify d3 tree graph to use a different data model, and here's where I'd really appreciate expert opinions. Following is a simple representation of what I think the data model could be. One is hierarchical model and the other is flat. Has anyone actually meddled with d3 tree data model? Any help/opinions are greatly appreciated! Thanks in advance for the help!
var hierarchicalData = [
{
"id": "n1",
"children": [
{
"id": "n1-a",
"children":[
{
"id": "n1-a-1"
}
]
},
{
"id": "n1-b",
"children":[
{
"id": "n1-b-1"
}
]
}
]
},
{
"id": "n2",
"children": [
{
"id": "n2-a",
"children":[
{
"id": "n2-a-1"
}
]
}
]
}
];
The following is a flat representation of the exact same hierarchical model but contains "level" that represents hierarchy.
{
"n1":{
"level": 0,
"children": ["n1-a", "n1-b"],
},
"n1-a":{
"level": 1,
"children":["n1-a-1"]
},
"n1-a-1":{
"level": 2,
"children":[]
},
"n1-b":{
"level": 1,
"children":["n1-b-1"]
},
"n1-b-1":{
"level": 2,
"children":[]
},
"n2":{
"level": 0,
"children": ["n2-a"]
},
"n2-a":{
"level": 1,
"children": ["n2-a-1"]
},
"n2-a-1":{
"level": 2,
"children":[]
}
}

Answer 1

If a child node can have more than one parent, then it's not a tree graph by definition.
There are several UI approaches you may take if you want to have a tree but it really depends on what you're trying to accomplish.
I worked with d3 tree to present a company Org-chart.
Several companies have employees with a direct manager and secondary manager.
What we did is showing the connection only to the direct manager.
But we presented the link to the other manager on mouse-over on the employee node.
This is more of a UI solution than a data model solution and there are many other possibilities.
Another option is to do what My-heritage did with family tree. They're showing both parents of each node, but only one of them is connected to the rest of the tree presented.